Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the 1-D Poisson equation for EC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with non-fusing hydrogen-1. The deuterium rates are consistent with predictions from the model.

Two simplified modeling approaches are used to model the combustion of Hydrazinium Nitroformate (HNF, N{sub 2}H{sub 5}-C(NO{sub 2}){sub 3}). The condensed phase is treated by high activation energy asymptotics. The gas phase is treated by two limit cases: the classical high activation energy, and the recently introduced low activation energy approach. This results in simplification of the gas phase energy equation, making an (approximate) analytical solution possible. The results of both models are compared with experimental results of HNF combustion. It is shown that the low activation energy approach yields better agreement with experimental observations (e.g. regression rate and temperature sensitivity), than the high activation energy approach.

How fast do fluvial landscapes approach steadystate after an application of tectonic or climatic perturbation? While theory and some numerical models predict that the celerity of the advective wave (knickpoint) controls the response time for perturbations, experiments and other landscape evolution models demonstrate that the time to steadystate is much longer than the theoretically predicted response time. We posit that the longevity of transient features and the time to steadystate are controlled by the stability of the topology and geometry of channel networks. Evolution of a channel network occurs by a combination of discrete capture events and continuous migration of water divides, processes, which are difficult to represent accurately in landscape evolution models. We therefore address the question of the time to steadystate using the DAC landscape evolution model that solves accurately for the location of water divides, using a combination of analytical solution for hillslopes and low-order channels together with a numerical solution for higher order channels. DAC also includes an explicit capture criterion. We have tested fundamental predictions from DAC and show that modeled networks reproduce natural network characteristics such as the Hack's exponent and coefficient and the fractal dimension. We define two steady-state criteria: a topographic steadystate, defined by global, pointwise steady elevation, and a topological steadystate defined as the state in which no further reorganization of the drainage network takes place. Analyzing block uplift simulations, we find that the time to achieve either topographic or topological steadystate exceeds by an order of magnitude the theoretical response time of the fluvial network. The longevity of the transient state is the result of the area feedback, by which, migration of a divide changes the local contributing area. This change propagates downstream as a slope adjustment, forcing further divide migrations

A study is being conducted to explore use of the steadystate visual-evoke electrocortical response as an indicator of cognitive task loading. Application of linear descriptive modeling to steadystate Visual Evoked Response (VER) data is summarized. Two aspects of linear modeling are reviewed: (1) unwrapping the phase-shift portion of the frequency response, and (2) parsimonious characterization of task-loading effects in terms of changes in model parameters. Model-based phase unwrapping appears to be most reliable in applications, such as manual control, where theoretical models are available. Linear descriptive modeling of the VER has not yet been shown to provide consistent and readily interpretable results.

The steadystates of cells affect their response to perturbation. Indeed, diagnostic markers for predicting the response to therapeutic perturbation are often based on steadystate measurements. In spite of this, no method exists to systematically characterize the relationship between steadystate and response. Mathematical models are established tools for studying cellular responses, but characterizing their relationship to the steadystate requires that it have a parametric, or analytical, expression. For some models, this expression can be derived by the King-Altman method. However, King-Altman requires that no substrate act as an enzyme, and is therefore not applicable to most models of signal transduction. For this reason we developed py-substitution, a simple but general method for deriving analytical expressions for the steadystates of mass action models. Where the King-Altman method is applicable, we show that py-substitution yields an equivalent expression, and at comparable efficiency. We use py-substitution to study the relationship between steadystate and sensitivity to the anti-cancer drug candidate, dulanermin (recombinant human TRAIL). First, we use py-substitution to derive an analytical expression for the steadystate of a published model of TRAIL-induced apoptosis. Next, we show that the amount of TRAIL required for cell death is sensitive to the steadystate concentrations of procaspase 8 and its negative regulator, Bar, but not the other procaspase molecules. This suggests that activation of caspase 8 is a critical point in the death decision process. Finally, we show that changes in the threshold at which TRAIL results in cell death is not always equivalent to changes in the time of death, as is commonly assumed. Our work demonstrates that an analytical expression is a powerful tool for identifying steadystate determinants of the cellular response to perturbation. All code is available at http://signalingsystems.ucsd.edu/models-and-code/ or

A steady-state CO/sub 2/ lase model is reported which can be used to predict and evaluate the performance of cw slow-flow and no-flow CO/sub 2/ lasers. Traditional CO/sub 2/ laser models require the solution of several simultaneous differential equations and can be used to model pulsed and fast-flow lasers in addition to cw and slow-flow devices. The model reported here is computationally simpler, requiring only a routine to solve one equation in one unknown, but is only useful for lasers which operate in the steadystate.

We study the nonequilibrium steadystate of a stochastic lattice gas model, originally proposed by Katz, Lebowitz and Spohn (Phys. Rev. B 28: 1655 (1983)). Firstly, we solve the model on some small lattices exactly in order to see the general dependence of the steadystate upon different parameters of the model. Nextly, we derive some analytical results for infinite lattice systems by taking some suitable limits. We then present some renormalization group results for the continuum version of the model via field theoretical techniques, the supersymmetry of the critical dynamics in zero field is also explored. Finally, we report some very recent 3-D Monte Carlo simulation results, which have been obtained by applying Multi-Spin-Coding techniques on a CDC vector supercomputer - Cyber 205 at John von Neumann Center.

The observed steady-state behavioral dynamics supported by unsignaled periods of reinforcement within repeating 2,000-s trials were modeled with a linear transfer function. These experiments employed improved schedule forms and analytical methods to improve the precision of the measured transfer function, compared to previous work. The refinements include both the use of multiple reinforcement periods that improve spectral coverage and averaging of independently determined transfer functions. A linear analysis was then used to predict behavior observed for three different test schedules. The fidelity of these predictions was determined. PMID:11831782

The quantitative analysis of biochemical reactions and metabolites is at frontier of biological sciences. The recent availability of high-throughput technology data sets in biology has paved the way for new modelling approaches at various levels of complexity including the metabolome of a cell or an organism. Understanding the metabolism of a single cell and multi-cell organism will provide the knowledge for the rational design of growth conditions to produce commercially valuable reagents in biotechnology. Here, we demonstrate how equations representing steadystate mass conservation, energy conservation, the second law of thermodynamics, and reversible enzyme kinetics can be formulated as a single system of linear equalities and inequalities, in addition to linear equalities on exponential variables. Even though the feasible set is non-convex, the reformulation is exact and amenable to large-scale numerical analysis, a prerequisite for computationally feasible genome scale modelling. Integrating flux, concentration and kinetic variables in a unified constraint-based formulation is aimed at increasing the quantitative predictive capacity of flux balance analysis. Incorporation of experimental and theoretical bounds on thermodynamic and kinetic variables ensures that the predicted steadystate fluxes are both thermodynamically and biochemically feasible. The resulting in silico predictions are tested against fluxomic data for central metabolism in E. coli and compare favourably with in silico prediction by flux balance analysis. PMID:20230840

The quantitative analysis of biochemical reactions and metabolites is at frontier of biological sciences. The recent availability of high-throughput technology data sets in biology has paved the way for new modelling approaches at various levels of complexity including the metabolome of a cell or an organism. Understanding the metabolism of a single cell and multi-cell organism will provide the knowledge for the rational design of growth conditions to produce commercially valuable reagents in biotechnology. Here, we demonstrate how equations representing steadystate mass conservation, energy conservation, the second law of thermodynamics, and reversible enzyme kinetics can be formulated as a single system of linear equalities and inequalities, in addition to linear equalities on exponential variables. Even though the feasible set is non-convex, the reformulation is exact and amenable to large-scale numerical analysis, a prerequisite for computationally feasible genome scale modelling. Integrating flux, concentration and kinetic variables in a unified constraint-based formulation is aimed at increasing the quantitative predictive capacity of flux balance analysis. Incorporation of experimental and theoretical bounds on thermodynamic and kinetic variables ensures that the predicted steadystate fluxes are both thermodynamically and biochemically feasible. The resulting in silico predictions are tested against fluxomic data for central metabolism in Escherichia coli and compare favourably with in silico prediction by flux balance analysis. PMID:20230840

A reactor model has been developed to simulate the steady-state of an industrial fluid catalytic cracking unit using a three-lump kinetic expression with parameters estimated from experiments in a microactivity test reactor. The model considers a transported bed reactor (riser) where gas-oil and catalyst are in contact to perform the endothermic cracking reactions, interacting with a two-phase moving bed regenerator with recirculation where the combustion of the coke deposited on the catalyst takes place. The model is used to find best operating conditions for maximizing gasoline yield in terms of gas-oil feed temperature (To) and recycled catalyst to gas-oil ratio (C/O). 12 refs., 4 figs.

In the context of changing climate, global pan evaporation records have shown a spatially-averaged trend of ∼ -2 to ∼ -3 mm a-2 over the past 30-50 years. This global phenomenon has motivated the development of the "PenPan" model (Rotstayn et al., 2006). However, the original PenPan model has yet to receive an independent experimental evaluation. Hence, we constructed an instrumented US Class A pan at Canberra Airport (Australia) and monitored it over a three-year period (2007-2010) to uncover the physics of pan evaporation under non-steadystate conditions. The experimental investigations of pan evaporation enabled theoretical formulation and parameterisation of the aerodynamic function considering the wind, properties of air and (with or without) the bird guard effect. The energy balance investigation allowed for detailed formulation of the short- and long-wave radiation associated with the albedos and the emissivities of the pan water surface and the pan wall. Here, we synthesise and generalise those earlier works to develop a new model called the "PenPan-V2" model for application under steadystate conditions (i.e., uses a monthly time step). Two versions (PenPan-V2C and PenPan-V2S) are tested using pan evaporation data available across the Australian continent. Both versions outperformed the original PenPan model with better representation of both the evaporation rate and the underlying physics of a US Class A pan. The results show the improved solar geometry related calculations (e.g., albedo, area) for the pan system led to a clear improvement in representing the seasonal cycle of pan evaporation. For general applications, the PenPan-V2S is simpler and suited for applications including an evaluation of long-term trends in pan evaporation.

Scenario modelling for the demonstration fusion reactor (DEMO) has been carried out using a variety of simulation codes. Two DEMO concepts have been analysed: a pulsed tokamak, characterized by rather conventional physics and technology assumptions (DEMO1) and a steady-state tokamak, with moderately advanced physics and technology assumptions (DEMO2). Sensitivity to impurity concentrations, radiation, and heat transport models has been investigated. For DEMO2, the impact of current driven non-inductively by neutral beams has been studied by full Monte Carlo simulations of the fast ion distribution. The results obtained are a part of a more extensive research and development (R&D) effort carried out in the EU in order to develop a viable option for a DEMO reactor, to be adopted after ITER for fusion energy research.

We consider an epidemical model within socially interacting mobile individuals to study the behaviors of steadystates of epidemic propagation in 2D networks. Using mean-field approximation and large scale simulations, we recover the usual epidemic behavior with critical thresholds δc and pc below which infectious disease dies out. For the population density δ far above δc, it is found that there is linear relationship between contact rate λ and the population density δ in the main. At the same time, the result obtained from mean-field approximation is compared with our numerical result, and it is found that these two results are similar by and large but not completely the same.

Treatment of air streams contaminated with binary volatile organic compound (VOC) mixtures in classical biofilters under steady-state conditions of operation was described with a general mathematical model. The model accounts for potential kinetic interactions among the pollutants, effects of oxygen availability on biodegradation, and biomass diversification in the filter bed. While the effects of oxygen were always taken into account, two distinct cases were considered for the experimental model validation. The first involves kinetic interactions, but no biomass differentiation, used for describing data from biofiltration of benzene/toluene mixtures. The second case assumes that each pollutant is treated by a different type of biomass. Each biomass type is assumed to form separate patches of biofilm on the solid packing material, thus kinetic interference does not occur. This model was used for describing biofiltration of ethanol/butanol mixtures. Experiments were performed with classical biofilters packed with mixtures of peat moss and perlite (2:3, volume:volume). The model equations were solved through the use of computer codes based on the fourth-order Runge-Kutta technique for the gas-phase mass balances and the method of orthogonal collocation for the concentration profiles in the biofilms. Good agreement between model predictions and experimental data was found in almost all cases. Oxygen was found to be extremely important in the case of polar VOCs (ethanol/butanol).

This paper presents the derivation of a simplified one dimensional (1D) steadystate pressure drop model for flow through a porous liquid acquisition device (LAD) inside a cryogenic propellant tank. Experimental data is also presented from cryogenic LAD tests in liquid hydrogen (LH2) and liquid oxygen (LOX) to compare against the simplified model and to validate the model at cryogenic temperatures. The purpose of the experiments was to identify the various pressure drop contributions in the analytical model which govern LAD channel behavior during dynamic, steadystate outflow. LH2 pipe flow of LAD screen samples measured the second order flow-through-screen (FTS) pressure drop, horizontal LOX LAD outflow tests determined the relative magnitude of the third order frictional and dynamic losses within the channel, while LH2 inverted vertical outflow tests determined the magnitude of the first order hydrostatic pressure loss and validity of the full 1Dmodel. When compared to room temperature predictions, the FTS pressure drop is shown to be temperature dependent, with a significant increase in flow resistance at LH2 temperatures. Model predictions of frictional and dynamic losses down the channel compare qualitatively with LOX LADs data. Meanwhile, the 1Dmodel predicted breakdown points track the trends in the LH2 inverted outflow experimental results, with discrepancies being due to a non-uniform injection velocity across the LAD screen not accounted for in the model.

A general first-principles model of the steadystate response of metal oxide gas sensors was developed by the authors and applied to the case of both electrochemical and resistive type oxygen sensors. It can describe many features of the experimentally observed response of commercial electrochemical zirconia sensors exposed to non-equilibrium gas mixtures consisting of O{sub 2} and one or more reducing species (CO, H{sub 2} , etc). However, the calculated sensor emf as a function of R`= 2p{sub O2}/P{sub CO} (or 2p{sub O2}/P{sub H2}) always showed a sharp transition from high to low values at some R` value and had a small value for R` >> 1. These results do not agree with the broad transitions and relatively high emf values for large R`, as observed experimentally at low temperatures. This paper discusses an extension of the model which is able to describe all aspects of the observed response.

Every airless body in the solar system is surrounded by a cloud of ejecta produced by the impact of interplanetary meteoroids on its surface [1]. Such ``dust exospheres'' have been observed around the Galilean satellites of Jupiter [2,3]. The prospect of long-term robotic and human operations on the Moon by the US and other countries has rekindled interest on the subject [4]. This interest has culminated with the - currently ongoing - investigation of the Moon's dust exosphere by the LADEE spacecraft [5]. Here a model is presented of a ballistic, collisionless, steadystate population of ejecta launched vertically at randomly distributed times and velocities and moving under constant gravity. Assuming a uniform distribution of launch times I derive closed form solutions for the probability density functions (pdfs) of the height distribution of particles and the distribution of their speeds in a rest frame both at the surface and at altitude. The treatment is then extended to particle motion with respect to a moving platform such as an orbiting spacecraft. These expressions are compared with numerical simulations under lunar surface gravity where the underlying ejection speed distribution is (a) uniform (b) a power law. I discuss the predictions of the model, its limitations, and how it can be validated against near-surface and orbital measurements.[1] Gault, D. Shoemaker, E.M., Moore, H.J., 1963, NASA TN-D 1767. [2] Kruger, H., Krivov, A.V., Hamilton, D. P., Grun, E., 1999, Nature, 399, 558. [3] Kruger, H., Krivov, A.V., Sremcevic, M., Grun, E., 2003, Icarus, 164, 170. [4] Grun, E., Horanyi, M., Sternovsky, Z., 2011, Planetary and Space Science, 59, 1672. [5] Elphic, R.C., Hine, B., Delory, G.T., Salute, J.S., Noble, S., Colaprete, A., Horanyi, M., Mahaffy, P., and the LADEE Science Team, 2014, LPSC XLV, LPI Contr. 1777, 2677.

Oxygen levels in cancerous tissue can have a significant effect on treatment response: hypoxic tissue is both more radioresistant and more chemoresistant than well-oxygenated tissue. While recent advances in medical imaging have facilitated real-time observation of macroscopic oxygenation, the underlying physics limits the resolution to the millimetre domain, whereas oxygen tension varies over a micrometre scale. If the distribution of oxygen in the tumour micro-environment can be accurately estimated, then the effect of potential dose escalation to these hypoxic regions could be better modelled, allowing more realistic simulation of biologically adaptive treatments. Reaction-diffusion models are commonly used for modelling oxygen dynamics, with a variety of functional forms assumed for the dependence of oxygen consumption rate (OCR) on cellular status and local oxygen availability. In this work, we examine reaction-diffusion models of oxygen consumption in spherically and cylindrically symmetric geometries. We consider two different descriptions of oxygen consumption: one in which the rate of consumption is constant and one in which it varies with oxygen tension in a hyperbolic manner. In each case, we derive analytic approximations to the steady-state oxygen distribution, which are shown to closely match the numerical solutions of the equations and accurately predict the extent to which oxygen can diffuse. The derived expressions relate the limit to which oxygen can diffuse into a tissue to the OCR of that tissue. We also demonstrate that differences between these functional forms are likely to be negligible within the range of literature estimates of the hyperbolic oxygen constant, suggesting that the constant consumption rate approximation suffices for modelling oxygen dynamics for most values of OCR. These approximations also allow the rapid identification of situations where hyperbolic consumption forms can result in significant differences from constant

We investigate the character and stability of stationary states of the (1 + 1) D evolution equation ∂t h +h3hxxx +h2∂x γ x = 0 describing the motion of an interface h (x , t) separating a thin warm viscous film from a thin cool inviscid layer where γ = γ (h) represents the interfacial tension. The phase diagram corresponding to all positive periodic steadystates (PPSS) is specified by two variables - the global extrema of the equilibrum shape and a generalized mechanical interface pressure. The analytic forms describing the PPSS shapes, the minimal period, the average height and the generalized free energy are all confirmed numerically. We find there is at most one non-trivial PPSS for specified period and volume. We also find no stable perturbed PPSS near the critical point for volume conserving perturbations of identical period. A weakly non-linear analysis about the critical point yields bifurcations of the pitchfork-type. For all non-trivial PPSS, we verify the unstable nature of the PPSS by transforming the non-normal operator (resulting from the spatially inhomogeneous PPSS) to normal form, which we then solve by finite element computations.

We investigate the stationary states of the (1 + 1) D equation ht +h3hxxx +h2γx (h) x = 0 for thin films of thickness h (x , t) where x is the spatial variable and t is time. The variable γ (h) , denotes the surface tension along the gas/liquid interface of the slender bilayer confined between two substrates enforcing thermal conduction within the gap. Equilibrium solutions include flat films, droplets, trenches/ridges and positive periodic steadystates (PPSS), the latter conveniently parameterized by a generalized interfacial pressure and the global extremum in shape. We derive perturbative solutions describing PPSS shapes near the stability threshold including their minimal period, average height and free energy. Weakly nonlinear analysis confirms that flat films always undergo a supercritical unstable pitch-fork bifurcation. Globally, our numerical simulations indicate at most one non-trivial PPSS per given period and volume. The free energy of droplet states is also always lower than the relevant corresponding PPSS, suggesting that initial flat films tend to redistribute mass into droplet-like configurations. By solving the linearized eigenvalue problem, we also confirm the unstable nature of PPSS solutions far from the stability threshold.

Steady-state analysis is performed on the kinetic model for the switch complex of the flagellar motor of Halobacterium salinarum (Nutsch et al.). The existence and uniqueness of a positive steady-state of the system is established and it is demonstrated why the steady-state is centered around the competent phase, a state of the motor in which it is able to respond to light stimuli. It is also demonstrated why the steady-state shifts to the refractory phase when the steady-state value of the response regulator CheYP increases. This work is one aspect of modeling in systems biology wherein the mathematical properties of a model are established. PMID:19857501

In this paper, we are presenting a model for electrophoretic motion of a charged particle through the membrane before it reaches the steadystate, based on concepts of Physics. Some results from analysis of the model are discussed.

Presented in this paper is a procedure to develop a high fidelity quasi steady-state aerodynamic model for use in race car vehicle dynamic simulations. Developed to fit quasi steady-state wind tunnel data, the aerodynamic model is regressed against three independent variables: front ground clearance, rear ride height, and yaw angle. An initial dual range model is presented and then further refined to reduce the model complexity while maintaining a high level of predictive accuracy. The model complexity reduction decreases the required amount of wind tunnel data thereby reducing wind tunnel testing time and cost. The quasi steady-state aerodynamic model for the pitch moment degree of freedom is systematically developed in this paper. This same procedure can be extended to the other five aerodynamic degrees of freedom to develop a complete six degree of freedom quasi steady-state aerodynamic model for any vehicle.

Steadystate1-D analytical solutions to estimate groundwater fluxes from temperature profiles are an attractive option because they are simple to apply, with no complex boundary or initial conditions. Steadystate solutions have been applied to estimate both aquifer scale fluxes as well as to estimate groundwater discharge to streams. This study explores the sources of uncertainty in flux estimates from regional scale aquifers caused by sensor precision, aquifer heterogeneity, multidimensional flow and variations in surface temperature due to climate change. Synthetic temperature profiles were generated using 2-D groundwater flow and heat transport models with homogeneous and heterogeneous hydraulic and thermal properties. Temperature profiles were analyzed assuming temperature can be determined with a precision between 0.1°C and 0.001°C. Analysis of synthetic temperature profiles show that the Bredehoeft and Papadopulos (1965) method can provide good estimates of the mean vertical Darcy flux over the length of the temperature profile. Reliable flux estimates were obtained when the ratio of vertical to horizontal flux was as low as 0.1, and in heterogeneous media, providing that temperature at the upper boundary was constant in time. However, temporal increases in surface temperature led to over-estimation of fluxes. Overestimates increased with time since the onset of, and with the rate of surface warming. Overall, the Bredehoeft and Papadopulos (1965) method may be more robust for the conditions with constant temperature distributions than previously thought, but that transient methods that account for surface warming should be used to determine fluxes in shallow aquifers.

An exact, closed-form analytical solution is derived for one-dimensional (1D), coupled, steady-state advection-dispersion equations with sequential first-order degradation of three dissolved species in groundwater. Dimensionless and mathematical analyses are used to examine the sensitivity of longitudinal dispersivity in the parent and daughter analytical solutions. The results indicate that the relative error decreases to less than 15% for the 1D advection-dominated and advection-dispersion analytical solutions of the parent and daughter when the Damköhler number of the parent decreases to less than 1 (slow degradation rate) and the Peclet number increases to greater than 6 (advection-dominated). To estimate first-order daughter product rate constants in advection-dominated zones, 1D, two-dimensional (2D), and three-dimensional (3D) steady-state analytical solutions with zero longitudinal dispersivity are also derived for three first-order sequentially degrading compounds. The closed form of these exact analytical solutions has the advantage of having (1) no numerical integration or evaluation of complex-valued error function arguments, (2) computational efficiency compared to problems with long times to reach steadystate, and (3) minimal effort for incorporation into spreadsheets. These multispecies analytical solutions indicate that BIOCHLOR produces accurate results for 1Dsteady-state, applications with longitudinal dispersion. Although BIOCHLOR is inaccurate in multidimensional applications with longitudinal dispersion, these multidimensional multispecies analytical solutions indicate that BIOCHLOR produces accurate steady-state results when the longitudinal dispersion is zero. As an application, the 1D advection-dominated analytical solution is applied to estimate field-scale rate constants of 0.81, 0.74, and 0.69/year for trichloroethene, cis-1,2-dichloroethene, and vinyl chloride, respectively, at the Harris Palm Bay, FL, CERCLA site. PMID:21883193

To predict glycolytic oscillations, Goldbeter and Lefever [Biophys. J. 12, 1302 (1972)] proposed a complex allosteric model, consisting of 14 species and 32 reactions. Under the usual assumption of a quasisteady state for all the enzymatic forms, they simplified it to a two-variable model and ruled out the possibility of multiple steadystates. In this work, the original network is determined to admit multiplicity of steadystates by a zero eigenvalue analysis. It is shown that the existence of the multiplicity in the original network can be determined by a subnetwork with five species and eight reactions. The fourteen-species network can be treated as containing four such subnetworks. The analysis is extended to a general modified allosteric model, consisting of n active subunits. It can be shown that the general network has no steady-state multiplicity if all the four subnetworks follow the case of n=1; otherwise, multiple steadystates can occur.

Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization. PMID:27243005

Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization. PMID:27243005

This paper studies the existence, uniqueness and convergence to non-equilibrium steadystates in Kac's model with an external coupling. We work in both Fourier distances and Wasserstein distances. Our methods work in the case where the external coupling is not a Maxwellian equilibrium. This provides an example of a non-equilibrium steadystate. We also study the behaviour as the number of particles goes to infinity and show quantitative estimates on the convergence rate of the first marginal.

Describes how microcomputer spreadsheets are easily adapted for use in groundwater modeling. Presents spreadsheet set-ups and the results of five groundwater models. Suggests that this approach can provide a basis for demonstrations, laboratory exercises, and student projects. (ML)

Numerical cochlear models are constructed by means of a finite element approach and their frequency and spatial responses are calculated. The cochlea is modelled as a coupled fluid-membrane system, for which both two- and three-dimensional models are considered. The fluid in the scala canals is assumed to be incompressible and the basilar membrane is assumed to be a locally reactive impedance wall or a lossy elastic membrane. With the three-dimensional models, the effects are examined of the spiral configuration of the cochlea, of the presence of the lamina and the ligament that narrows the coupling area between the two fluid canals (scala vestibuli and scala tympani), and of the extended reaction of the basilar membrane which cannot be included in case of the two-dimensional models. The conclusion is that these effects on the cochlear response and the inherent mechanism governing the cochlear behaviour are found to be rather secondary.

A simple model for the combustion of solid monopropellants is presented. The condensed phase is treated by high activation energy asymptotics. The gas phase is treated by two limit cases: high activation energy, and low activation energy. This results in simplification of the gas phase energy equation, making an (approximate) analytical solution possible. The results of the model are compared with experimental results of Hydrazinium Nitroformate (HNF) combustion.

We report computational results from a model for prebiotic evolution.The model is schematic, but contains a correct description of thebasic statistical problem associated with understanding how the initiation of life can occur given the strong entropic barriers (sometimesknown as 'Eigen's paradox' and appearing in experiments as the 'tar problem'). The model is similar to one of the modelsintroduced years ago by Kauffman and coworkers. The important innovationwhich we introduce is imposition of the requirement that, to qualifyas a lifelike dynamical chemical system, the system must not be inchemical equilibrium. That constraint turns out to have major qualitativeeffects on the conclusions. In particular, very sparse chemical networksturn out to be the most favorable ones for generating autocatalyticnonequilibrium states. This suggests qualitatively that deserts might bebetter than ponds for initiating life. Some details of the models andsimulations will be described, including recent results in which weintroduce spatial diffusion and a proxy for temperature into the description ofthe model chemistry. Results on growth rates, convergence and theoverall probability of generation of lifelike states as a function ofparameters of the chemical network model will be presented.

A reduced model of a completely stirred-tank bioreactor coupled to a settling tank with recycle is analyzed in its steadystates. In the reactor, the concentrations of one dominant particulate biomass and one soluble substrate component are modelled. While the biomass decay rate is assumed to be constant, growth kinetics can depend on both substrate and biomass concentrations, and optionally model substrate inhibition. Compressive and hindered settling phenomena are included using the Bürger-Diehl settler model, which consists of a partial differential equation. Steady-state solutions of this partial differential equation are obtained from an ordinary differential equation, making steady-state analysis of the entire plant difficult. A key result showing that the ordinary differential equation can be replaced with an approximate algebraic equation simplifies model analysis. This algebraic equation takes the location of the sludge-blanket during normal operation into account, allowing for the limiting flux capacity caused by compressive settling to easily be included in the steady-state mass balance equations for the entire plant system. This novel approach grants the possibility of more realistic solutions than other previously published reduced models, comprised of yet simpler settler assumptions. The steady-state concentrations, solids residence time, and the wastage flow ratio are functions of the recycle ratio. Solutions are shown for various growth kinetics; with different values of biomass decay rate, influent volumetric flow, and substrate concentration. PMID:26476681

The model was developed as a part of the study, "Advanced Fuel Cycles and Waste Management", which was performed during 20032005 by an ad-hoc expert group under the Nuclear Development Committee in the OECD/NEA. The model was designed for an efficient conduct of nuclear fuel cycle scheme cost analyses. It is simple, transparent and offers users the capability to track down the cost analysis results. All the fuel cycle schemes considered in the model aremore » represented in a graphic format and all values related to a fuel cycle step are shown in the graphic interface, i.e., there are no hidden values embedded in the calculations. All data on the fuel cycle schemes considered in the study including mass flows, waste generation, cost data, and other data such as activities, decay heat and neutron sources of spent fuel and highlevel waste along time are included in the model and can be displayed. The user can modify easily the values of mass flows and/or cost parameters and see the corresponding changes in the results. The model calculates: frontend fuel cycle mass flows such as requirements of enrichment and conversion services and natural uranium; mass of waste based on the waste generation parameters and the mass flow; and all costs. It performs Monte Carlo simulations with changing the values of all unit costs within their respective ranges (from lower to upper bounds).« less

Version 00 SMAFS was developed as a part of the study, "Advanced Fuel Cycles and Waste Management", which was performed during 2003-2005 by an ad-hoc expert group under the Nuclear Development Committee in the OECD/NEA. The model was designed for an efficient conduct of nuclear fuel cycle scheme cost analyses. It is simple, transparent and offers users the capability to track down cost analysis results. All the fuel cycle schemes considered in the model aremore » represented in a graphic format and all values related to a fuel cycle step are shown in the graphic interface, i.e., there are no hidden values embedded in the calculations. All data on the fuel cycle schemes considered in the study including mass flows, waste generation, cost data, and other data such as activities, decay heat and neutron sources of spent fuel and high-level waste along time are included in the model and can be displayed. The user can easily modify values of mass flows and/or cost parameters and see corresponding changes in the results. The model calculates: front-end fuel cycle mass flows such as requirements of enrichment and conversion services and natural uranium; mass of waste based on the waste generation parameters and the mass flow; and all costs.« less

A diffusive energy-balance climate model, governed by a nonlinear parabolic partial differential equation, was studied. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. Models similar to the main one are considered, and the number of their steadystates was determined. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The stability under small perturbations of the main model's climates was investigated. A stability criterion is derived, and its application shows that the present climate and the deep freeze are stable, whereas the model's glacial is unstable. The dependence was examined of the number of steadystates and of their stability on the average solar radiation.

This work provides a description of the solvatochromic effect in terms of a hard-sphere model taking into account the microscopic parameters of the solution. The average energies of the solute-solvent system were calculated for Franck-Condon and relaxed states assuming pairwise electrostatic interactions between polarizable, dipolar molecules contained in clusters made of 1-solute and 10-solvent molecules. This in turn allowed us to estimate the values of the solvatochromic shifts. The dependence of these shifts on temperature and electronic properties of molecules expressed in terms of their polarity and polarizability was investigated. PMID:24226908

Seasonal variations of firn density in ice-sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn. A recent high-resolution (mm scale) density profile, measured along a 181 m core from Antarctica, showed small-scale density variations with a clear seasonal cycle that apparently was not-related to seasonal variations in deposition or known near-surface processes (Gerland and others 1999). A recent model of surface elevation changes (Zwally and Li, submitted) produced a seasonal variation in firn densification, and explained the seasonal surface elevation changes observed by satellite radar altimeters. In this study, we apply our 1-D time-dependent numerical model of firn densification that includes a temperature-dependent formulation of firn densification based on laboratory measurements of grain growth. The model is driven by a steady-state seasonal surface temperature and a constant accumulation rate appropriate for the measured Antarctic ice core. The modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid-summer with the highest temperature history compress to the highest density, and the layers deposited during later summer to autumn with the lowest temperature history compress to the lowest density. The initial amplitude of the seasonal difference of about 0.13 reduces to about 0.09 in five years and asymptotically to 0.92 at depth, which is consistent with the core measurements.

Stochastic analyses were performed to examine sequential first-order monomolecular reactions at the microscopic scale and both Fickian and non-Fickian plume reactive transport at the macroscopic scale. An analytical solution was derived for the chemical master equation (CME) for a closed system of irreversible first-order monomolecular reactions. Taking a Lagrangian reference frame of particles migrating from a source, analyses show that the relative concentration of each species in the deterministic analytical solution for 1-Dsteadystate plug flow with first-order sequential degradation is mathematically equivalent to the mean of a multinomial distribution of plume particles moving at constant velocity with sequential transformations described by transition probabilities of a discrete state, continuous-time Markov chain. In order to examine the coupling of reaction and transport terms in subdiffusive-reactive transport equations, a closed-form multispecies analytical solution also was derived for steadystate advection, dispersion, and sequential first-order reaction. Using a 1-D continuous-time random walk (CTRW) embedded in Markov chains, computationally efficient Monte Carlo simulations of particle movement were performed to more fully examine effects of subdiffusive-reactive transport with an application to steadystate, sequentially degrading multispecies plumes at a site in Palm, Bay, FL. The simulation results indicated that non-Fickian steadystate plumes can resemble Fickian plumes because linear reactions truncate the waiting time between particle jumps, which removes lower velocity particles from the broad spectrum of velocities in highly heterogeneous media. Results show that fitting of Fickian models to plume concentration data can lead to inaccurate estimates of rate constants because of the wide distribution of travel times in highly heterogeneous media.

A user's guide for the steady-state thermoregulatory model is presented. The model was modified to provide conversational interaction on a remote terminal, greater flexibility for parameter estimation, increased efficiency of convergence, greater choice of output variable and more realistic equations for respiratory and skin diffusion water losses.

In this paper, based on the slow time varying function theory, dynamical equations for the amplitude and phase of the dynamic atomic force microscope are derived. Then, the sensitivity of the amplitude and phase to the dissipative and conservative parts of interaction force is investigated. The most advantage of this dynamical model is the ability to simulate and analysis the dynamics behavior of amplitude and phase of the AFM tip motion not only in the steadystate but also in the transient regime. Using numerical analysis the transient and steadystate behavior of amplitude and phase is studied and the sensitivity of amplitude and phase to the interaction force is analyzed. PMID:27448201

Widely-used forms of the K-epsilon turbulence model are shown to yield arbitrary steady-state converged solutions that are highly dependent on numerical considerations such as initial conditions and solution procedure. These solutions contain pseudo-laminar regions of varying size. By applying a nullcline analysis to the equation set, it is possible to clearly demonstrate the reasons for the anomalous behavior. In summary, the degenerate solution acts as a stable fixed point under certain conditions, causing the numerical method to converge there. The analysis also suggests a methodology for preventing the anomalous behavior in steady-state computations.

Recent theoretical work on the cooperative equilibrium binding of myosin subfragment-1-ADP to regulated actin, as influenced by Ca2+, is extended here to the cooperative steady-state ATPase activity of myosin subfragment-1 on regulated actin. Exact solution of the general steady-state problem will require Monte Carlo calculations. Three interrelated special cases are discussed in some detail and sample computer (not Monte Carlo) solutions are given. The eventual objective is to apply these considerations to in vitro experimental data and to in vivo muscle models. PMID:6455170

We present a translation and analysis of an unpublished manuscript by Albert Einstein in which he attempted to construct a `steady-state' model of the universe. The manuscript, which appears to have been written in early 1931, demonstrates that Einstein once explored a cosmic model in which the mean density of matter in an expanding universe is maintained constant by the continuous formation of matter from empty space. This model is very different to previously known Einsteinian models of the cosmos (both static and dynamic) but anticipates the later steady-state cosmology of Hoyle, Bondi and Gold in some ways. We find that Einstein's steady-statemodel contains a fundamental flaw and suggest that it was abandoned for this reason. We also suggest that he declined to explore a more sophisticated version because he found such theories rather contrived. The manuscript is of historical interest because it reveals that Einstein debated between steady-state and evolving models of the cosmos decades before a similar debate took place in the cosmological community.

Travel-time based models simplify the description of reactive transport by replacing the spatial coordinates with the groundwater travel time, posing a quasi one-dimensional (1-D) problem and potentially rendering the determination of multidimensional parameter fields unnecessary. While the approach is exact for strictly advective transport in steady-state flow if the reactive properties of the porous medium are uniform, its validity is unclear when local-scale mixing affects the reactive behavior. We compare a two-dimensional (2-D), spatially explicit, bioreactive, advective-dispersive transport model, considered as "virtual truth", with three 1-D travel-time based models which differ in the conceptualization of longitudinal dispersion: (i) neglecting dispersive mixing altogether, (ii) introducing a local-scale longitudinal dispersivity constant in time and space, and (iii) using an effective longitudinal dispersivity that increases linearly with distance. The reactive system considers biodegradation of dissolved organic carbon, which is introduced into a hydraulically heterogeneous domain together with oxygen and nitrate. Aerobic and denitrifying bacteria use the energy of the microbial transformations for growth. We analyze six scenarios differing in the variance of log-hydraulic conductivity and in the inflow boundary conditions (constant versus time-varying concentration). The concentrations of the 1-Dmodels are mapped to the 2-D domain by means of the kinematic (for case i), and mean groundwater age (for cases ii & iii), respectively. The comparison between concentrations of the "virtual truth" and the 1-D approaches indicates extremely good agreement when using an effective, linearly increasing longitudinal dispersivity in the majority of the scenarios, while the other two 1-D approaches reproduce at least the concentration tendencies well. At late times, all 1-Dmodels give valid approximations of two-dimensional transport. We conclude that the

Travel-time based models simplify the description of reactive transport by replacing the spatial coordinates with the groundwater travel time, posing a quasi one-dimensional (1-D) problem and potentially rendering the determination of multidimensional parameter fields unnecessary. While the approach is exact for strictly advective transport in steady-state flow if the reactive properties of the porous medium are uniform, its validity is unclear when local-scale mixing affects the reactive behavior. We compare a two-dimensional (2-D), spatially explicit, bioreactive, advective-dispersive transport model, considered as "virtual truth", with three 1-D travel-time based models which differ in the conceptualization of longitudinal dispersion: (i) neglecting dispersive mixing altogether, (ii) introducing a local-scale longitudinal dispersivity constant in time and space, and (iii) using an effective longitudinal dispersivity that increases linearly with distance. The reactive system considers biodegradation of dissolved organic carbon, which is introduced into a hydraulically heterogeneous domain together with oxygen and nitrate. Aerobic and denitrifying bacteria use the energy of the microbial transformations for growth. We analyze six scenarios differing in the variance of log-hydraulic conductivity and in the inflow boundary conditions (constant versus time-varying concentration). The concentrations of the 1-Dmodels are mapped to the 2-D domain by means of the kinematic (for case i), and mean groundwater age (for cases ii & iii), respectively. The comparison between concentrations of the "virtual truth" and the 1-D approaches indicates extremely good agreement when using an effective, linearly increasing longitudinal dispersivity in the majority of the scenarios, while the other two 1-D approaches reproduce at least the concentration tendencies well. At late times, all 1-Dmodels give valid approximations of two-dimensional transport. We conclude that the

An approach to the integrated modelling of plasma regimes in the projected neutron source DEMO-FNS based on different codes is developed. The consistency check of the steady-state regime is carried out, namely, the possibility of the plasma current ramp-up, acceptance of growth rates of MHD modes in the steady-state regime, heat loads to the wall and divertor plates and neutron yield value. The following codes are employed for the integrated modelling. ASTRA transport code for calculation of plasma parameters in the steady-state regime, NUBEAM Monte Carlo code for NBI incorporated into the ASTRA code, DINA free boundary equilibrium and evolution code, SPIDER free boundary equilibrium and equilibrium reconstruction code, KINX ideal MHD stability code, TOKSTAB rigid shift vertical stability code, edge and divertor plasma B2SOLPS5.2 code and Semi-analytic Hybrid Model (SHM) code for self-consistent description of the core, edge and divertor plasmas based on the experimental scaling laws. The consistent steady-state regime for the DEMO-FNS plasma and the plasma current ramp-up scenario are developed using the integrated modelling approach. Passive copper coils are suggested to reduce the plasma vertical instability growth rate to below ˜30 s-1.The outer divertor operation in the ‘high-recycling’ regime is numerically demonstrated with a maximal heat flux density of 7-9 MW m-2 that is technically acceptable.

Prognostics is the process of predicting a system's future states, health degradation/wear, and remaining useful life (RUL). This information plays an important role in preventing failure, reducing downtime, scheduling maintenance, and improving system utility. Prognostics relies heavily on wear estimation. In some components, the sensors used to estimate wear may not be fast enough to capture brief transient states that are indicative of wear. For this reason it is beneficial to be capable of detecting and estimating the extent of component wear using steady-state measurements. This paper details a method for estimating component wear using steady-state measurements, describes how this is used to predict future states, and presents a case study of a current/pressure (I/P) Transducer. I/P Transducer nominal and off-nominal behaviors are characterized using a physics-based model, and validated against expected and observed component behavior. This model is used to map observed steady-state responses to corresponding fault parameter values in the form of a lookup table. This method was chosen because of its fast, efficient nature, and its ability to be applied to both linear and non-linear systems. Using measurements of the steadystate output, and the lookup table, wear is estimated. A regression is used to estimate the wear propagation parameter and characterize the damage progression function, which are used to predict future states and the remaining useful life of the system.

The steady-state and dynamic-state discharge processes have been discussed to develop a superconducting magnetic energy storage (SMES) model in the paper. The SMES model allows the integrated analysis and optimization of the SMES devices, and their control systems, and can also serve as an independent storage module in the practical SMES application circuits, thus provide a method to link superconductivity technology to conventional power electronics in a SMES device.

In this paper, we have developed an efficient wavelet based approximation method to biofilm model under steadystate arising in enzyme kinetics. Chebyshev wavelet based approximation method is successfully introduced in solving nonlinear steadystate biofilm reaction model. To the best of our knowledge, until now there is no rigorous wavelet based solution has been addressed for the proposed model. Analytical solutions for substrate concentration have been derived for all values of the parameters δ and SL. The power of the manageable method is confirmed. Some numerical examples are presented to demonstrate the validity and applicability of the wavelet method. Moreover the use of Chebyshev wavelets is found to be simple, efficient, flexible, convenient, small computation costs and computationally attractive. PMID:26661721

Steady-state and dynamic models are developed to study the physical mechanisms that determine the pushing or engulfment of a solid particle at a moving solid-liquid interface. The mathematical model formulation rigorously accounts for energy and momentum conservation, while faithfully representing the interfacial phenomena affecting solidification phase change and particle motion. A numerical solution approach is developed using the Galerkin finite element method and elliptic mesh generation in an arbitrary Lagrangian-Eulerian implementation, thus allowing for a rigorous representation of forces and dynamics previously inaccessible by approaches using analytical approximations. We demonstrate that this model accurately computes the solidification interface shape while simultaneously resolving thin fluid layers around the particle that arise from premelting during particle engulfment. We reinterpret the significance of premelting via the definition an unambiguous critical velocity for engulfment from steady-state analysis and bifurcation theory. We also explore the complicated transient behaviors that underlie the steadystates of this system and posit the significance of dynamical behavior on engulfment events for many systems. We critically examine the onset of engulfment by comparing our computational predictions to those obtained using the analytical model of Rempel and Worster [29]. We assert that, while the accurate calculation of van der Waals repulsive forces remains an open issue, the computational model developed here provides a clear benefit over prior models for computing particle drag forces and other phenomena needed for the faithful simulation of particle engulfment.

The steady-state turning of a bicycle arises when the bicycle/rider system negotiates a constant radius turn with constant speed and roll angle. This paper explores steady-state turning by employing a bicycle instrumented to measure steering torque, steering angle, and bicycle speed, acceleration, and angular velocity. We report data obtained from 134 trials using two subjects executing steady turns defined by nine different radii, three speeds, and three rider lean conditions. A model for steady-state turning, based on the Whipple bicycle model, is used to interpret the experimental results. Overall, the model explains 95.6% of the variability in the estimated bicycle roll angle, 99.4% of the variability in the measured steering angle, and 6.5% of the variability in the measured steering torque. However, the model explains 56.6% of the variability in steering torque for the subset of trials without exaggerated rider lean relative to the bicycle frame. Thus, the model, which assumes a rigid and non-leaning rider, reasonably predicts bicycle roll and steering angles for all rider lean conditions and steering torque without exaggerated rider lean. The findings demonstrate that lateral shifting of the bicycle/rider centre of mass strongly influences the steering torque, suggesting that rider lean plays an important role in bicycle control during steady-state turning. By contrast, the required steering angle is largely insensitive to rider lean, suggesting that the steering angle serves as a superior cue for bicycle control relative to the steering torque.

A recent study discussed the steady-statemodel for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model—the low-energy Maxwellian core with an energy range of tens of eV, the intermediate ∼102–103 eV energy-range (“halo”) electrons, and the high ∼103–105 eV energy-range (“super-halo”) electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (∼102 Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave–particle resonance with higher-frequency electrostatic fluctuations in the Langmuir frequency range (∼105 Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.

A recent study discussed the steady-statemodel for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model—the low-energy Maxwellian core with an energy range of tens of eV, the intermediate ˜102–103 eV energy-range (“halo”) electrons, and the high ˜103–105 eV energy-range (“super-halo”) electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (˜102 Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave–particle resonance with higher-frequency electrostatic fluctuations in the Langmuir frequency range (˜105 Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.

Catania (2005) found that a computational model of the operant reserve (Skinner, 1938) produced realistic behavior in initial, exploratory analyses. Although Catania's operant reserve computational model demonstrated potential to simulate varied behavioral phenomena, the model was not systematically tested. The current project replicated and extended the Catania model, clarified its capabilities through systematic testing, and determined the extent to which it produces behavior corresponding to matching theory. Significant departures from both classic and modern matching theory were found in behavior generated by the model across all conditions. The results suggest that a simple, dynamic operant model of the reflex reserve does not simulate realistic steadystate behavior. PMID:21238552

Nutrient levels in coastal waters must be accurately assessed to determine the nutrient effects of increasing populations on coastal ecosystems. To accomplish this goal, in-field data with sufficient temporal resolution are required to define nutrient sources and sinks, and to ultimately calculate nutrient budgets. Models then are required for the interpretation and analysis of data sets. To quantify the coastal ocean nitrogen input to Yaquina Bay, Oregon, nitrate concentrations were measured by a moored sensor hourly for one month during summer upwelling some distance outside the estuary entrance jetties. The time series results then were interpreted using a steadystatemodel (Visual Plumes' PDSW) and a hydrodynamic model, the Finite Volume Coastal Ocean Model (FVCOM). The physical scales of many stream and river plumes often lie between the scales for outfall mixing zone plume models, such as those found in EPA's Visual Plumes, and larger-sized grid scales for regional circulation models like FVCOM. A potential advantage of relatively simple, steadystate plume models is that they use entrainment terms to close the plume equations, theory that has proven useful in simulating turbulent plume discharges from various sources, some approaching the dimensions of rivers. Important advantages of models like FVCOM are that they are dynamic and include the effects of the Earth's rotation. The results showed that the steady-state plume model simulates observed velocity and concentration data fairly well during periods of strong discharge velocity and weak ambient coastal currents. FVCOM was judged to give better estimates under all other ambient current conditions, although the data from the mooring cannot be used to prove this assertion as stronger currents would deflect the plume away from the mooring. Nevertheless, plume models may be useful in establishing boundary and initial conditions for hydrodynamic models.

A ubiquitiformal model for the one-dimensional steady-state heat transfer of a cellular material rod is developed in this paper, and the explicit analytical expressions for both the temperature distribution and the equivalent thermal conductivity are obtained. The calculated results for two kinds of dry soil are found to be in good agreement with previous experimental data. Moreover, it is demonstrated that the ubiquitiformal model is more reasonable for describing such a cellular material than the fractal one, and hence a ubiquitiformal rather than a fractal model should be considered in practical applications whenever the integral dimensional measure of a real physical object must be taken into account.

A steady-state lean combustion model for monolithic catalytic combustors is given. The model, consisting of several semi-global chemical reaction steps in the gas-phase and on the surface, is capable of analyzing CO and THC emissions. In the model computation presented, the influence of operating and design parameters on the minimum combustor length is studied. Special attention is given to the effect of after-bed gas-phase reaction space. Comparison with experimental data indicates good agreement in the range of parameters covered.

We undertake here a systematic study of the rheology of blood in steady-state shear flows. As blood is a complex fluid, the first question that we try to answer is whether, even in steady-state shear flows, we can model it as a rheologically simple fluid, i.e., we can describe its behavior through a constitutive model that involves only local kinematic quantities. Having answered that question positively, we then probe as to which non-Newtonian model best fits available shear stress vs shear-rate literature data. We show that under physiological conditions blood is typically viscoplastic, i.e., it exhibits a yield stress that acts as a minimum threshold for flow. We further show that the Casson model emerges naturally as the best approximation, at least for low and moderate shear-rates. We then develop systematically a parametric dependence of the rheological parameters entering the Casson model on key physiological quantities, such as the red blood cell volume fraction (hematocrit). For the yield stress, we base our description on its critical, percolation-originated nature. Thus, we first determine onset conditions, i.e., the critical threshold value that the hematocrit has to have in order for yield stress to appear. It is shown that this is a function of the concentration of a key red blood cell binding protein, fibrinogen. Then, we establish a parametric dependence as a function of the fibrinogen and the square of the difference of the hematocrit from its critical onset value. Similarly, we provide an expression for the Casson viscosity, in terms of the hematocrit and the temperature. A successful validation of the proposed formula is performed against additional experimental literature data. The proposed expression is anticipated to be useful not only for steady-state blood flow modeling but also as providing the starting point for transient shear, or more general flow modeling.

Closed form, analytical solutions to the problem of steady-state heat transfer in living tissue modeled as cylindrical shells are presented and discussed. These solutions are particularly useful for the study of temperature distributions in the extremities. Metabolic heat generation, conduction, and heat transported by the blood perfusing the tissue are considered in the model. The results demonstrate the important role that the blood stream plays in the transfer of heat inside living tissue. Solutions are also presented for the limiting cases of diminishing blood flow that would occur during vasoconstriction or occlusion of blood by external means.

Eigen model of molecular evolution is popular in studying complex biological and biomedical systems. Using the Hamilton-Jacobi equation method, we have calculated analytic equations for the steadystate distribution of the Eigen model with a relative accuracy of O(1/N), where N is the length of genome. Our results can be applied for the case of small genome length N, as well as the cases where the direct numerics can not give accurate result, e.g., the tail of distribution.

We present a quasi-steadystate reduction of a linear reaction-hyperbolic master equation describing the directed intermittent search for a hidden target by a motor-driven particle moving on a one-dimensional filament track. The particle is injected at one end of the track and randomly switches between stationary search phases and mobile nonsearch phases that are biased in the anterograde direction. There is a finite possibility that the particle fails to find the target due to an absorbing boundary at the other end of the track. Such a scenario is exemplified by the motor-driven transport of vesicular cargo to synaptic targets located on the axon or dendrites of a neuron. The reduced model is described by a scalar Fokker-Planck (FP) equation, which has an additional inhomogeneous decay term that takes into account absorption by the target. The FP equation is used to compute the probability of finding the hidden target (hitting probability) and the corresponding conditional mean first passage time (MFPT) in terms of the effective drift velocity V, diffusivity D, and target absorption rate λ of the random search. The quasi-steadystate reduction determines V, D, and λ in terms of the various biophysical parameters of the underlying motor transport model. We first apply our analysis to a simple 3-state model and show that our quasi-steadystate reduction yields results that are in excellent agreement with Monte Carlo simulations of the full system under physiologically reasonable conditions. We then consider a more complex multiple motor model of bidirectional transport, in which opposing motors compete in a "tug-of-war", and use this to explore how ATP concentration might regulate the delivery of cargo to synaptic targets. PMID:20169417

Establishment of near steady-state high-performance discharges with internal transport barriers in the electron and ion heat and the toroidal momentum channels is investigated using the GLF23 and Weiland confinement models. A combination of neutral beam and electron cyclotron heating and current drive is used to optimally shape the current profile for near non-inductive steady-state operation. The GLF23 and Weiland confinement models have had some success in modeling DIII-D discharges and consequently represents our best choice for DIII-D AT scenario development at this time. By starting the modeling with actual high-performance DIII-D discharges, we expect to obtain experimentally realized results. The stability of our simulations is monitored with the BALOO and GATO codes and rf heating and current drive is modelled with TORAY-GA. This computationally instensive modeling approach requires concurrent computing methods in order to be used routinely. We discuss our efforts to date in producing a parallel computational transport environment.

We study periodically driven bosonic scalar field theories in the infinite N limit. It is well known that the free theory can undergo parametric resonance under monochromatic modulation of the mass term and thereby absorb energy indefinitely. Interactions in the infinite N limit terminate this increase for any choice of the UV cutoff and driving frequency. The steadystate has nontrivial correlations and is synchronized with the drive. The O (N ) model at infinite N provides the first example of a clean interacting quantum system that does not heat to infinite temperature at any drive frequency.

Groundwater modeling has become a vital component to water supply and contaminant transport investigations. An important component of groundwater modeling under steadystate conditions is selecting a representative hydraulic conductivity (K) estimate or set of estimates which defines the K field of the studied region. Currently, there are a number of characterization approaches to obtain K at various scales and in varying degrees of detail, but there is a paucity of information in terms of which characterization approach best predicts flow through aquifers or drawdowns caused by some drawdown inducing events. The main objective of this paper is to assess K estimates obtained by various approaches by predicting drawdowns from independent cross-hole pumping tests and total flow rates through a synthetic heterogeneous aquifer from flow-through tests. Specifically, we (1) characterize a synthetic heterogeneous aquifer built in the sandbox through various techniques (permeameter analyses of core samples, single-hole, cross-hole, and flow-through testing), (2) obtain mean K fields through traditional analysis of test data by treating the medium to be homogeneous, (3) obtain heterogeneous K fields through kriging and steadystate hydraulic tomography, and (4) conduct forward simulations of 16 independent pumping tests and six flowthrough tests using these homogeneous and heterogeneous K fields and comparing them to actual data. Results show that the mean K and heterogeneous K fields estimated through kriging of small-scale K data (core and single-hole tests) yield biased predictions of drawdowns and flow rates in this synthetic heterogeneous aquifer. In contrast, the heterogeneous K distribution or ?K tomogram? estimated via steadystate hydraulic tomography yields excellent predictions of drawdowns of pumping tests not used in the construction of the tomogram and very good estimates of total flow rates from the flowthrough tests. These results suggest that steadystate

The increase in Type 2 diabetes and other metabolic disorders has led to an intense focus on the areas of research related to metabolism. Because the liver is essential in regulating metabolite concentrations that maintain life, it is especially important to have good knowledge of the functions within this organ. In silico mathematical models that can adequately describe metabolite concentrations, flux and transport rates in the liver in vivo can be a useful predictive tool. Fully dynamic models, which contain expressions for Michaelis-Menten reaction kinetics can be utilized to investigate different metabolic states, for example exercise, fed or starved state. In this paper we describe a two compartment (blood and tissue) spatially lumped liver metabolism model. First, we use Bayesian Flux Balance Analysis (BFBA) to estimate the values of flux and transport rates at steadystate, which agree closely with values from the literature. These values are then used to find a set of Michaelis-Menten parameters and initial concentrations which identify a dynamic model that can be used for exploring different metabolic states. In particular, we investigate the effect of doubling the concentration of lactate entering the system via the hepatic artery and portal vein. This change in lactate concentration forces the system to a new steadystate, where glucose production is increased.

In UO2 pellets irradiated in standard water reactor, Xe nano-bubbles nucleate, grow, coarsen and finally reach a quasi steadystate size distribution: transmission electron microscope (TEM) observations typically report a concentration around 10-4 nm-3 and a radius around 0.5 nm. This phenomenon is often considered as a consequence of radiation enhanced diffusion, precipitation of gas atoms and ballistic mixing. However, in UO2 thin foils irradiated with energetic ions at room temperature, a nano-void population whose size distribution reaches a similar steadystate can be observed, although quasi no foreign atoms are implanted nor significant cation vacancy diffusion expected in conditions. Atomistic simulations performed at low temperature only address the first stage of the process, supporting the assumption of void heterogeneous nucleation: 25 keV sub-cascades directly produce defect aggregates (loops and voids) even in the absence of gas atoms and thermal diffusion. In this work a semi-empirical stochastic model is proposed to enlarge the time scale covered by simulation up to damage levels where every point in the material undergoes the superposition of a large number of sub-cascade impacts. To account for the accumulation of these impacts, simple rules inferred from the atomistic simulation results are used. The model satisfactorily reproduces the TEM observations of nano-voids size and concentration, which paves the way for the introduction of a more realistic damage term in rate theory models.

An experimental and mechanistic-modeling study is reported for the transient flow of aqueous foam through 1.3-{mu}m{sup 2} (1.3-D) Boise sandstone at backpressures in excess of 5 MPa (700 psi) over a quality range from 0.80 to 0.99. Total superficial velocities range from as little as 0.42 to 2.20 m/day (1.4 ft/day to 7 ft/day). Sequential pressure taps and gamma-ray densitometry measure flow resistance and in-situ liquid saturations, respectively. We garner experimental pressure and saturation profiles in both the transient and steadystates. Adoption of a mean-size foam-bubble conservation equation along with the traditional reservoir simulation equations allows mechanistic foam simulation. Since foam mobility depends heavily upon its texture, the bubble population balance is both useful and necessary as the role of foam texture must be incorporated into any model which seeks accurate prediction of flow properties. Our model employs capillary-pressure-dependent kinetic expressions for lamellae generation and coalescence and also a term for trapping of lamellae. Additionally, the effects of surfactant chemical transport are included. We find quantitative agreement between experimental and theoretical saturation and pressure profiles in both the transient and steadystates.

A steady-state, horizontally homogeneous, cloud-topped marine boundary layer model based primarily on the work of Lilly (1968) and Schubert et al., (1979) is presented. The conservative thermodynamic variables are equivalent potential temperature, theta(sub e), and total water mixing ratio, q + l. Some of the differences between this and Lilly's (1968) model are: radiation is allowed to penetrate into the boundary layer; cloud top values of longwave radiation, equivalent potential temperature, and water vapor mixing ratio are linear functions of height derived from climatological data at California coastal stations; and the closure assumption assumes a weighted average of Lilly's (1968) maximum and minimum entrainment theories. This model was programmed in FORTRAN and will run interactively on an IBM-compatible personal computer. The program allows the user to specify the geographical location, the wind speed, the sea-surface temperature, the large scale horizontal divergence, and the initial guess for cloud top height. Output includes the steadystate values of cloud top and cloud base height, mixed layer equivalent potential temperature and total water mixing ratio, and the associated convective and radiative fluxes.

A pseudo-one-dimensional channel model has been developed to estimate gas production from underground coal gasification. The model incorporates a zero-dimensional steady-state cavity growth submodel and models mass transfer from the bulk gas to the coal wall using a correlation for natural convection. Simulations with the model reveal that the gas calorific value is sensitive to coal reactivity and the exposed reactive surface area per unit volume in the channel. A comparison of model results with several small-scale field trials conducted at Centralia in the U.S.A. show that the model can make good predictions of the gas production and composition under a range of different operating conditions, including operation with air and steam/oxygen mixtures. Further work is required to determine whether the model formulation is also suitable for simulating large-scale underground coal gasification field trials.

The interface geometry of freshwater lenses in layered aquifers was investigated by physical 2D laboratory experiments. The resulting steady-state geometries of the lenses were compared to existing analytical expressions from Dupuit-Ghyben-Herzberg (DGH) analysis of strip-island lenses for various cases of heterogeneity. Despite the vertical exaggeration of the physical models, which would seem to vitiate the assumption of vertical equipotentials, the fits with the DGH models were generally satisfactory. Observed deviations between the analytical and physical models can be attributed mainly to outflow zones along the shore line, which are not considered in the analytical models. As unconfined natural lenses have small outflow zones compared to their overall dimensions, and flow is mostly horizontal, the DGH analytical models should perform even better at full scale. Numerical models that do consider the outflow face generally gave a good fit to the physical models.

This paper is devoted to studying a reaction-diffusion-chemotaxis model with a volume-filling effect in a bounded domain with Neumann boundary conditions. We first establish the global existence of classical solutions bounded uniformly in time. Then applying the asymptotic analysis and bifurcation theory, we obtain both the local and global structure of steadystates bifurcating from the homogeneous steadystates in one dimension by treating the chemotactic coefficient as a bifurcation parameter. Moveover we find the stability criterion of the bifurcating steadystates and give a sufficient condition for the stability of steadystates with small amplitude. The pattern formation of the model is numerically shown and the stability criterion is verified by our numerical simulations.

Some of the gross characteristics of the rupture processes for the 1966 Parkfield, 1979 Imperial Valley, and 1980 Mexicali Valley earthquakes are determined by waveform inversion of near-source data employing a steadystate dislocation model in a layered half-space. The forward model involves a piecewise-linear rupture front moving with a constant horizontal rupture velocity on a fault of infinite length and finite width. The inferred shapes for the rupture front and for the distribution of slip as a function of depth are consistent with previous results obtained by use of more general models. The results obtained show that a strong velocity pulse observed in the nearsource region can be modeled as the passage of the rupture front phase and that the supershear propagation of the rupture front in the sedimentary layers of the medium provides a mechanism for the generation of the observed large amplitudes.

A computer program, based on a one-dimensional mathematical model which predicts the stream water-quality response characteristics from waste source inputs, is described and documented. Variables predicted include dissolved oxygen, biochemical oxygen demand, nitrogen forms, total and fecal-coliform bacteria, orthophosphate-phosphorus, and various conservative substances. The model is based primarily on the Streeter-Phelps oxygen-sag equation. Special options of the program include the capability of handling nonpont source waste inputs and anoxic conditions. The model formulation is based on a steady-state assumption which requires constant flow rate of waste and stream discharges and associated parameters. To achieve a problem solution, each reach of a stream system is broken into a given number of subreaches, generally defined by locations of waste or tributary inflow points. All waste constituents are assumed to be completely mixed within any cross section. (Woodard-USGS)

A two-dimensional steadystate heat transfer model is developed in this report for the thermoplastic pultrusion process. In this model, the finite element method with a stream line diffusion approach is used. The stream line diffusion method will minimize the numerical oscillations when the pulling speed is high and the finite element mesh is coarse. The crystallization kinetics reported by Ozawa is employed to calculate the relative crystallinity and the heat released due to the crystallization process during cooling. It is assumed the taper angle of the consolidation die is small so that the pultrusion can be approximated as an orthotropic material. The volume fractions of void, matrix, and fiber are defined based on material densities and consolidation strains. Examples for pultrusion of APC-2 are studied using this finite element model.

The surface water model EXWAT is applied to monitoring studies of hazardous substances to estimate site-specific emissions from measured concentrations. The model includes the main processes which govern the fate of chemicals in rivers, namely, advection, volatility, degradation processes, sedimentation, resuspension, and protonic equilibria. The steady-state solution of the linear mass balance equations leads to proportionality between input and concentration of a chemical, which is used to assess input rates from measured concentrations. Subsequently, the model can be used for pollution control and identification of unknown releases. With measured concentrations in the Rhine near Koblenz (95 km downstream from the mouth of the river Main) the load of dichloromethane from the tributary Main was estimated. The comparison with measured concentrations in the tributary mouth has a good agreement in this case.

Nonlinear Noisy Leaky Integrate and Fire (NNLIF) models for neurons networks can be written as Fokker-Planck-Kolmogorov equations on the probability density of neurons, the main parameters in the model being the connectivity of the network and the noise. We analyse several aspects of the NNLIF model: the number of steadystates, a priori estimates, blow-up issues and convergence toward equilibrium in the linear case. In particular, for excitatory networks, blow-up always occurs for initial data concentrated close to the firing potential. These results show how critical is the balance between noise and excitatory/inhibitory interactions to the connectivity parameter. AMS Subject Classification: 35K60, 82C31, 92B20. PMID:22657097

Using the optimization method of Vecchia & Cooley (1987), nonlinear Scheffe??-type confidence intervals were calculated tor the parameters and the simulated heads of a steady-state groundwater flow model covering 450 km2 of a leaky aquifer. The nonlinear confidence intervals are compared to corresponding linear intervals. As suggested by the significant nonlinearity of the regression model, linear confidence intervals are often not accurate. The commonly made assumption that widths of linear confidence intervals always underestimate the actual (nonlinear widths was not correct for the head intervals. Results show that nonlinear effects can cause the nonlinear intervals to be offset from, and either larger or smaller than, the linear approximations. Prior information on some transmissivities helps reduce and stabilize the confidence intervals, with the most notable effects occurring for the parameters on which there is prior information and for head values in parameter zones for which there is prior information on the parameters.

In the subset of OB stars with large-scale, organized magnetic fields, the stellar wind is forced to flow along magnetic field lines and is trapped within a magnetosphere corotating with its host star. As the wind turns on itself, shocks heat the plasma to millions of degrees and produce X-ray emission. Such magnetospheres are typically classified with the "wind magnetic confinement parameter", a simplified ratio between the magnetic energy density and the wind kinetic energy density. This parameter is often used to estimate magnetosphere properties, such as size, mass-loss rate, and spin-down time. Unfortunately, the strong magnetic fields in magnetospheres (polar strength: 100 G - 10 kG) and resulting Alfven velocities make magnetohydrodynamics simulations computationally difficult due to very small timesteps. To get around this issue, we approximate a massive-star magnetosphere as a series of one-dimensional flows along magnetic dipole field lines and develop a steady-statemodel from the resulting hydrodynamic equations. With this model, we derive scaling relations for the stellar mass-loss rate as a function of surface colatitude and find agreement with previous scaling results derived from simulations. These relations are further extended to include the effects of rigid-body rotation within the magnetosphere. Additionally, we develop an X-ray emission model from this steady-state analysis and compare it against both the "XADM" model for X-ray emission from massive star magnetospheres and observations of massive magnetic stars. Finally, we discuss improvements to the traditional wind magnetic confinement parameter to take into account the effect of a magnetic field on the wind kinetic energy density.

Species dependent kinetic, transport and thermodynamic coefficients were employed in a one dimensional model of the premixed, laminar, steadystate ozone flame. Convenient expressions for these coefficients are reported. They are based on independent measurements, no arbitrary parameters are used. The governing equations are solved using a relaxation technique and the partial differential equation package, PDECOL. Species and temperature profiles and the burning velocities are found over the range of initial ozone mole fraction of 0.25 to 1.00. The computed burning velocities are no more than 30% greater than the measurements of Streng and Grosses. Comparison with the computed results of Warnatz shows agreement within + or - 12%, even though quite different expressions for some of the kinetic coefficients were used. These differences are most obvious in the atomic oxygen and temperature profiles at an initial ozone mole fraction of unity.

From complex biological systems to a simple simmering pot, thermodynamic systems held out of equilibrium are exceedingly common in nature. Despite this, a general theory to describe these types of phenomena remains elusive. In this talk, we explore a simple modification of the venerable Ising model in hopes of shedding some light on these issues. In both one and two dimensions, systems attached to two distinct heat reservoirs exhibit many of the hallmarks of phase transition. When such systems settle into a non-equilibrium steady-state they exhibit numerous interesting phenomena, including an unexpected ``freezing by heating.'' There are striking and surprising similarities between the behavior of these systems in one and two dimensions, but also intriguing differences. These phenomena will be explored and possible approaches to understanding the behavior will be suggested. Supported by the US National Science Foundation through Grants DMR-0904999, DMR-1205309, and DMR-1244666

Soil-atmosphere exchange is an important transport process influencing environmental fate and transport of many persistent organic pollutants (POPs). This study focuses on modelling the gaseous exchange of a semi-volatile polycyclic aromatic hydrocarbon (phenanthrene) between soil and the atmosphere using the multicomponent reactive transport code MIN3P. MIN3P is typically applied to simulate aqueous and vapor phase subsurface transport and reaction processes. We extended the code to also include an atmospheric boundary layer where eddy diffusion and photodegradation take place. The relevant processes and parameters affecting soil-atmosphere exchange were investigated in several scenarios and at various time scales. We found that phenanthrene is well-mixed in the atmospheric boundary layer under neutral or stable atmospheric conditions due to fast eddy diffusion. Uptake of airborne phenanthrene to soils is limited by the soil properties and initially depends on diffusion in soil gas and sorption to the solids. On the long term seepage water dominates transport into deeper soil layers; biodegradation finally leads to steady-state concentration profiles in the subsurface typically achieved after a few centuries. If concentrations in the atmosphere decrease, e.g. due to environmental legislation, then soils become sources for the POPs for the first two months and function as sinks again for the POPs until new steadystate concentrations are reached (after decades to centuries). MIN3P was also used to simulate diurnal soil-atmosphere exchanges of airborne pollutants due to temperature changes and photodegradation, both which cause fluctuations in atmospheric concentrations and therefore affect mass transfer between soil and the atmosphere. The model can further be applied to estimate the environmental fate of other POPs between soil and the atmosphere under different environmental pollution and climate change scenarios.

Hollow fiber modules are commonly used to conveniently and efficiently remove cryoprotective agents (CPAs) from cryopreserved cell suspensions. In this paper, a steady-statemodel coupling mass transfers across cell and hollow fiber membranes is theoretically developed to evaluate the removal of CPAs from cryopreserved blood using hollow fiber modules. This steady-statemodel complements the unsteady-state model which was presented in our previous study. As the steady-statemodel, unlike the unsteady-state model, can be used to evaluate the effect of ultrafiltration flow rates on the clearance of CPAs. The steady-statemodel is validated by experimental results and then is compared with the unsteady-state model. Using the steady-statemodel, the effects of ultrafiltration flow rates, NaCl concentrations in dialysate, blood flow rates and dialysate flow rates on CPA concentration variation and cell volume response are investigated in detail. According to the simulative results, the osmotic damage of red blood cells (RBCs) can easily be reduced by increasing ultrafiltration flow rates, increasing NaCl concentrations in dialysate, increasing blood flow rates or decreasing dialysate flow rates. PMID:20524740

A critical issue for sustaining high performance, negative central shear (NCS) discharges is the ability to maintain current distributions that are maximum off axis. Sustaining such hollow current profiles in steadystate requires the use of non-inductively driven current sources. On the DIII-D experiment, a combination of neutral beam current drive (NBCD) and bootstrap current have been used to create transient NCS discharges. The electron cyclotron heating (ECH) and current drive (ECCD) system is currently being upgraded from three gyrotrons to six to provide more than 3MW of absorbed power in long-pulse operation to help sustain the required off-axis current drive. This upgrade SuPporrs the long range goal of DIII-D to sustain high performance discharges with high values of normalized {beta}, {beta}{sub n} = {beta}/(I{sub p}/aB{sub T}), confinement enhancement factor, H, and neutron production rates while utilizing bootstrap current fraction, f{sub bs}, in excess of 50%. At these high performance levels, the likelihood of onset of MHD modes that spoil confinement indicates the need to control plasma profiles if we are to extend this operation to long pulse or steadystate. To investigate the effectiveness of the EC system and to explore operating scenarios to sustain these discharges, we use time-dependent simulations of the equilibrium, transport and stability. We explore methods to directly alter the safety factor profile, q, through direct current drive or by localized electron heating to modify the bootstrap current profile. Time dependent simulations using both experimentally determined [1] and theory-based [2] energy transport models have been done. Here, we report on simulations exploring parametric dependencies of the heating, current drive, and profiles that affect our ability to sustain stable discharges.

The fact that dependent variables of groundwater models are generally nonlinear functions of model parameters is shown to be a potentially significant factor in calculating accurate confidence intervals for both model parameters and functions of the parameters, such as the values of dependent variables calculated by the model. The Lagrangian method of Vecchia and Cooley [Vecchia, A.V. and Cooley, R.L., Water Resources Research, 1987, 23(7), 1237-1250] was used to calculate nonlinear Scheffe-type confidence intervals for the parameters and the simulated heads of a steady-state groundwater flow model covering 450 km2 of a leaky aquifer. The nonlinear confidence intervals are compared to corresponding linear intervals. As suggested by the significant nonlinearity of the regression model, linear confidence intervals are often not accurate. The commonly made assumption that widths of linear confidence intervals always underestimate the actual (nonlinear) widths was not correct. Results show that nonlinear effects can cause the nonlinear intervals to be asymmetric and either larger or smaller than the linear approximations. Prior information on transmissivities helps reduce the size of the confidence intervals, with the most notable effects occurring for the parameters on which there is prior information and for head values in parameter zones for which there is prior information on the parameters.The fact that dependent variables of groundwater models are generally nonlinear functions of model parameters is shown to be a potentially significant factor in calculating accurate confidence intervals for both model parameters and functions of the parameters, such as the values of dependent variables calculated by the model. The Lagrangian method of Vecchia and Cooley was used to calculate nonlinear Scheffe-type confidence intervals for the parameters and the simulated heads of a steady-state groundwater flow model covering 450 km2 of a leaky aquifer. The nonlinear confidence

We examine the performance of two steady-statemodels, a numerical solution of the advection-diffusion equation and the Gaussian plume-model-based AERMOD (the American Meteorological Society/Environmental Protection Agency Regulatory Model), to predict dispersion for surface releases under low wind-speed conditions. A comparison of model estimates with observations from two tracer studies, the Prairie Grass experiment and the Idaho Falls experiment indicates that about 50% of the concentration estimates are within a factor of two of the observations, but the scatter is large: the 95% confidence interval of the ratio of the observed to estimated concentrations is about 4. The model based on the numerical solution of the diffusion equation in combination with the model of Eckman (1994, Atmos Environ 28:265-272) for horizontal spread performs better than AERMOD in explaining the observations. Accounting for meandering of the wind reduces some of the overestimation of concentrations at low wind speeds. The results deteriorate when routine one-level observations are used to construct model inputs. An empirical modification to the similarity estimate of the surface friction velocity reduces the underestimation at low wind speeds.

We analyze a model for CO oxidation on surfaces which incorporates both rapid diffusion of adsorbed CO, and superlattice ordering of adsorbed immobile oxygen on a square lattice of adsorption sites. The superlattice ordering derives from an "eight-site adsorption rule," wherein diatomic oxygen adsorbs dissociatively on diagonally adjacent empty sites, provided that none of the six additional neighboring sites are occupied by oxygen. A "hybrid" formalism is applied to implement the model. Highly mobile adsorbed CO is assumed randomly distributed on sites not occupied by oxygen (which is justified if one neglects CO-CO and CO-O adspecies interactions), and is thus treated within a mean-field framework. In contrast, the distribution of immobile adsorbed oxygen is treated within a lattice-gas framework. Exact master equations are presented for the model, together with some exact relationships for the coverages and reaction rate. A precise description of steady-state bifurcation behavior is provided utilizing both conventional and "constant-coverage ensemble" Monte Carlo simulations. This behavior is compared with predictions of a suitable analytic pair approximation derived from the master equations. The model exhibits the expected bistability, i.e., coexistence of highly reactive and relatively inactive states, which disappears at a cusp bifurcation. In addition, we show that the oxygen superlattice ordering produces a symmetry-breaking transition, and associated coarsening phenomena, not present in conventional Ziff-Gulari-Barshad-type reaction models.

Molten salt parabolic trough system (MSPT) uses molten salt as heat transfer fluid (HTF) instead of synthetic oil. The demonstration plant of MSPT was constructed by Chiyoda Corporation and Archimede Solar Energy in Italy in 2013. Chiyoda Corporation developed a steady-statemodel for predicting the theoretical behavior of the demonstration plant. The model was designed to calculate the concentrated solar power and heat loss using ray tracing of incident solar light and finite element modeling of thermal energy transferred into the medium. This report describes the verification of the model using test data on the demonstration plant, detailed analyses on the relation between flow rate and temperature difference on the metal tube of receiver and the effect of defocus angle on concentrated power rate, for solar collector assembly (SCA) development. The model is accurate to an extent of 2.0% as systematic error and 4.2% as random error. The relationships between flow rate and temperature difference on metal tube and the effect of defocus angle on concentrated power rate are shown.

Recent progress on ITER steady-state (SS) scenario modelling by the ITPA-IOS group is reviewed. Code-to-code benchmarks as the IOS group's common activities for the two SS scenarios (weak shear scenario and internal transport barrier scenario) are discussed in terms of transport, kinetic profiles, and heating and current drive (CD) sources using various transport codes. Weak magnetic shear scenarios integrate the plasma core and edge by combining a theory-based transport model (GLF23) with scaled experimental boundary profiles. The edge profiles (at normalized radius rho = 0.8-1.0) are adopted from an edge-localized mode-averaged analysis of a DIII-D ITER demonstration discharge. A fully noninductive SS scenario is achieved with fusion gain Q = 4.3, noninductive fraction f(NI) = 100%, bootstrap current fraction f(BS) = 63% and normalized beta beta(N) = 2.7 at plasma current I(p) = 8MA and toroidal field B(T) = 5.3 T using ITER day-1 heating and CD capability. Substantial uncertainties come from outside the radius of setting the boundary conditions (rho = 0.8). The present simulation assumed that beta(N)(rho) at the top of the pedestal (rho = 0.91) is about 25% above the peeling-ballooning threshold. ITER will have a challenge to achieve the boundary, considering different operating conditions (T(e)/T(i) approximate to 1 and density peaking). Overall, the experimentally scaled edge is an optimistic side of the prediction. A number of SS scenarios with different heating and CD mixes in a wide range of conditions were explored by exploiting the weak-shear steady-state solution procedure with the GLF23 transport model and the scaled experimental edge. The results are also presented in the operation space for DT neutron power versus stationary burn pulse duration with assumed poloidal flux availability at the beginning of stationary burn, indicating that the long pulse operation goal (3000s) at I(p) = 9 MA is possible. Source calculations in these simulations have been

Alterations in neural synchrony and oscillations may contribute to the pathophysiology of schizophrenia and reflect aberrations in cortical glutamatergic and GABAergic neurotransmission. We tested the effects of a GABA agonist and a NMDA antagonist on auditory steadystate responses (ASSRs) in awake rats with neonatal ventral hippocampal lesions (NVHLs) as a neurodevelopmental model of schizophrenia. NVHL vs. SHAM lesioned rats were injected with saline then either ketamine (NMDA antagonist) or muscimol (GABAA agonist). Time-frequency analyses examined alterations in phase locking (consistency) across trials and changes in total power (magnitude). ASSRs were compared at 5 stimulation frequencies (10, 20, 30, 40, and 50 Hz). In SHAM rats, phase locking and power generally increased with stimulation frequency. Both ketamine and muscimol also increased phase locking and power in SHAM rats, but mostly in the 20 to 40 Hz range. NVHL and ketamine altered the frequency dependence of phase locking, while only ketamine changed power frequency dependence. Muscimol affected power, but not phase locking, in the NVHL rats. NVHL and ketamine models of schizophrenia produce similar independent effects on ASSR, potentially representing similar forms of cortical network/glutamatergic dysfunction, albeit the effects of ketamine were more robust. Muscimol produced NVHL-dependent reductions in ASSR measures, suggesting that cortical networks in this model are intolerant to post-synaptic GABAergic stimulation. These findings suggest the utility of combining lesion, pharmacological, and ASSR approaches in understanding neural mechanisms underlying disturbed synchrony in schizophrenia. PMID:22504207

Parameter sensitivity analysis is a powerful tool in the building and analysis of biochemical network models. For stochastic simulations, parameter sensitivity analysis can be computationally expensive, requiring multiple simulations for perturbed values of the parameters. Here, we use trajectory reweighting to derive a method for computing sensitivity coefficients in stochastic simulations without explicitly perturbing the parameter values, avoiding the need for repeated simulations. The method allows the simultaneous computation of multiple sensitivity coefficients. Our approach recovers results originally obtained by application of the Girsanov measure transform in the general theory of stochastic processes [A. Plyasunov and A. P. Arkin, J. Comput. Phys. 221, 724 (2007), 10.1016/j.jcp.2006.06.047]. We build on these results to show how the method can be used to compute steady-state sensitivity coefficients from a single simulation run, and we present various efficiency improvements. For models of biochemical signaling networks, the method has a particularly simple implementation. We demonstrate its application to a signaling network showing stochastic focussing and to a bistable genetic switch, and present exact results for models with linear propensity functions.

Actual problems in geotechnical design, e.g., of underground openings for radioactive waste repositories or high-pressure gas storages, require sophisticated constitutive models and consistent parameters for rock salt that facilitate reliable prognosis of stress-dependent deformation and associated damage. Predictions have to comprise the active mining phase with open excavations as well as the long-term development of the backfilled mine or repository. While convergence-induced damage occurs mostly in the vicinity of openings, the long-term behaviour of the backfilled system is dominated by the damage-free steady-state creep. However, because in experiments the time necessary to reach truly stationary creep rates can range from few days to years, depending mainly on temperature and stress, an innovative but simple creep testing approach is suggested to obtain more reliable results: A series of multi-step tests with loading and unloading cycles allows a more reliable estimate of stationary creep rate in a reasonable time. For modelling, we use the advanced strain-hardening approach of Günther-Salzer, which comprehensively describes all relevant deformation properties of rock salt such as creep and damage-induced rock failure within the scope of an unified creep ansatz. The capability of the combination of improved creep testing procedures and accompanied modelling is demonstrated by recalculating multi-step creep tests at different loading and temperature conditions. Thus reliable extrapolations relevant to in-situ creep rates (10^{-9} to 10^{-13} s^{-1}) become possible.

The purpose of this study was to provide a rigorous theoretical understanding of the dissolution behavior of dental enamel over the entire time-course of demineralization and to simulate by computer an erosion-type caries lesion according to the physical "hydroxyapatite model". The appropriate diffusion equations which account for simultaneous diffusion and equilibrium of all species in enamel pores, boundary layer, and bulk solution, and which also take into consideration surface reaction kinetics, were employed to allow for calculation of the micro-environmental solution concentration and changes in the mineral density as a function of time and distance within the enamel. This comprehensive physical model for non-steady-state enamel dissolution also explicitly takes into account changes in the diffusivity and the dissolution rate constant as a function of mineral density. Demineralization experiments were conducted in 0.1 mol/L sink acetate buffer (pH = 4.50, mu = 0.50), with ground bovine dental enamel blocks of known surface area mounted (with beeswax) in a rotating disk apparatus. Mineral density profiles were quantified by means of contact x-ray microradiography. The physical model was used to predict mineral density profiles for given demineralization treatments. The experimental profiles agreed quite well with the predicted profiles, when the effective diffusivity of the enamel was assumed to be a function of porosity and when changes in surface area of the crystallites were taken into consideration. PMID:3476613

Human activities are significantly altering biogeochemical cycles at the global scale, posing a significant problem for earth system models (ESMs), which may incorporate static land-use change inputs but do not actively simulate policy or economic forces. One option to address this problem is to couple an ESM with an economically oriented integrated assessment model. Here we have implemented and tested a coupling mechanism between the carbon cycles of an ESM (CESM, the Community Earth System Model) and an integrated assessment (GCAM) model, examining the best proxy variables to share between the models, and quantifying our ability to distinguish climate- and land-use-driven flux changes. The net primary production and heterotrophic respiration outputs of the Community Land Model (CLM), the land component of CESM, were found to be the most robust proxy variables by which to manipulate GCAM's assumptions of long-term ecosystem steadystate carbon, with short-term forest production strongly correlated with long-term biomass changes in climate-change model runs. Carbon-cycle effects of anthropogenic land-use change are short-term and spatially limited relative to widely distributed climate effects, and as a result we were able to distinguish these effects successfully in the model coupling, passing only the latter to GCAM. By allowing climate effects from a full earth system model to dynamically modulate the economic and policy decisions of an integrated assessment model, this work provides a foundation for linking these models in a robust and flexible framework capable of examining two-way interactions between human and earth system processes.

We described in this paper the development of a high fidelity vehicle aerodynamic model to fit wind tunnel test data over a wide range of vehicle orientations. We also present a comparison between the effects of this proposed model and a conventional quasi steady-state aerodynamic model on race vehicle simulation results. This is done by implementing both of these models independently in multi-body quasi steady-state simulations to determine the effects of the high fidelity aerodynamic model on race vehicle performance metrics. The quasi steadystate vehicle simulation is developed with a multi-body NASCAR Truck vehicle model, and simulations are conducted for three different types of NASCAR race tracks, a short track, a one and a half mile intermediate track, and a higher speed, two mile intermediate race track. For each track simulation, the effects of the aerodynamic model on handling, maximum corner speed, and drive force metrics are analysed. The accuracy of the high-fidelity model is shown to reduce the aerodynamic model error relative to the conventional aerodynamic model, and the increased accuracy of the high fidelity aerodynamic model is found to have realisable effects on the performance metric predictions on the intermediate tracks resulting from the quasi steady-state simulation.

We describe a framework for efficiently coupling the power output of a series-connected string of single-band-gap solar cells to an electrochemical process that produces storable fuels. We identify the fundamental efficiency limitations that arise from using solar cells with a single band gap, an arrangement that describes the use of currently economic solar cell technologies such as Si or CdTe. Steady-state equivalent circuit analysis permits modeling of practical systems. For the water-splitting reaction, modeling defines parameters that enable a solar-to-fuels efficiency exceeding 18% using laboratory GaAs cells and 16% using all earth-abundant components, including commercial Si solar cells and Co- or Ni-based oxygen evolving catalysts. Circuit analysis also provides a predictive tool: given the performance of the separate photovoltaic and electrochemical systems, the behavior of the coupled photovoltaic–electrochemical system can be anticipated. This predictive utility is demonstrated in the case of water oxidation at the surface of a Si solar cell, using a Co–borate catalyst.

The approach chosen to modelsteadystate scattering from jet engines with moving turbine blades is based upon the Finite Difference Time Domain (FDTD) method. The FDTD method is a numerical electromagnetic program based upon the direct solution in the time domain of Maxwell's time dependent curl equations throughout a volume. One of the strengths of this method is the ability to model objects with complicated shape and/or material composition. General time domain functions may be used as source excitations. For example, a plane wave excitation may be specified as a pulse containing many frequencies and at any incidence angle to the scatterer. A best fit to the scatterer is accomplished using cubical cells in the standard cartesian implementation of the FDTD method. The material composition of the scatterer is determined by specifying its electrical properties at each cell on the scatterer. Thus, the FDTD method is a suitable choice for problems with complex geometries evaluated at multiple frequencies. It is assumed that the reader is familiar with the FDTD method.

A high qmin (qmin > 2) operational scenario has been identified as a possible candidate to achieve ITER baseline goals. This scenario requires a broad current profile with high bootstrap fraction, which in turn requires a relatively large pedestal height. The goal of this study is to identify an operational space for ITER high-qmin steady-state scenarios via self-consistent integrated modeling using the IPS/FASTRAN framework with EPED providing the edge pedestal height. FASTRAN is an iterative numerical procedure that integrates a variety of models (transport, heating, CD, equilibrium and stability) and has been shown to reproduce most features of DIII-D high beta discharges with a stationary current profile. The FASTRAN solver has been implemented in the Integrated Plasma Simulator (IPS) framework. The sensitivity of this operating space to uncertainties in the transport and pedestal predictions will be studied. Work supported by the US Department of Energy under DE-AC05-00OR22725, DE-FC02-04ER54698, and DE-AC52-07NA27344.

A dipole model is presented for ion flow in excitable membranes. This model considers the membrane to be composed of two distinct regions: a polar region and a nonpolar region. Further, the construction of an electrodiffusive formalism which takes explicit account of the energy of partition required by an ion for passage from external fluid to nonpolar region is presented. In the polar region a cooperative effect is considered which produces a configurational transition of the polar group dependent only on membrane voltage. A resulting change in voltage drop across the polar group is brought about by this configurational transition. This gives rise to a negative steady-state resistance for the equimolar case, in reasonable agreement with observation. The theory, in addition, is in reasonable accord with nonequimolar ion flow, and provides an explanation for such effects as the following: the intercept of the voltage-current characteristic, the ion membrane concentrations inferred from electrodiffusion theories, and the effects of polyvalent cations PMID:5471696

Large gene regulatory networks (GRN) are often modeled with quasi-steady-state approximation (QSSA) to reduce the huge computational time required for intrinsic noise quantification using Gillespie stochastic simulation algorithm (SSA). However, the question still remains whether the stochastic QSSA model measures the intrinsic noise as accurately as the SSA performed for a detailed mechanistic model or not? To address this issue, we have constructed mechanistic and QSSA models for few frequently observed GRNs exhibiting switching behavior and performed stochastic simulations with them. Our results strongly suggest that the performance of a stochastic QSSA model in comparison to SSA performed for a mechanistic model critically relies on the absolute values of the mRNA and protein half-lives involved in the corresponding GRN. The extent of accuracy level achieved by the stochastic QSSA model calculations will depend on the level of bursting frequency generated due to the absolute value of the half-life of either mRNA or protein or for both the species. For the GRNs considered, the stochastic QSSA quantifies the intrinsic noise at the protein level with greater accuracy and for larger combinations of half-life values of mRNA and protein, whereas in case of mRNA the satisfactory accuracy level can only be reached for limited combinations of absolute values of half-lives. Further, we have clearly demonstrated that the abundance levels of mRNA and protein hardly matter for such comparison between QSSA and mechanistic models. Based on our findings, we conclude that QSSA model can be a good choice for evaluating intrinsic noise for other GRNs as well, provided we make a rational choice based on experimental half-life values available in literature. PMID:26327626

Background Stoichiometric models provide a structural framework for analyzing steady-state cellular behavior. Models are developed either through augmentations of existing models or more recently through automatic reconstruction tools. There is currently no standardized practice or method for validating the properties of a model before placing it in the public domain. Considerable effort is often required to understand a model’s inconsistencies before its reuse within new research efforts. Results We present a review of common issues in stoichiometric models typically uncovered during pathway analysis and constraint-based optimization, and we detail succinct and efficient ways to find them. We present MC3, Model and Constraint Consistency Checker, a computational tool that can be used for two purposes: (a) identifying potential connectivity and topological issues for a given stoichiometric matrix, S, and (b) flagging issues that arise during constraint-based optimization. The MC3 tool includes three distinct checking components. The first examines the results of computing the basis for the null space for Sv = 0; the second uses connectivity analysis; and the third utilizes Flux Variability Analysis. MC3 takes as input a stoichiometric matrix and flux constraints, and generates a report summarizing issues. Conclusions We report the results of applying MC3 to published models for several systems including Escherichia coli, an adipocyte cell, a Chinese Hamster Ovary cell, and Leishmania major. Several issues with no prior documentation are identified. MC3 provides a standalone MATLAB-based comprehensive tool for model validation, a task currently performed either ad hoc or implemented in part within other computational tools. PMID:24261865

The biological carbon pump, mediated principally via the sinking of organic matter from the surface ocean, is a significant term in the global carbon cycle. It transfers annually 5-15 GT C yr-1 out of the photic zone, an amount comparable to the annual accumulation of CO2 in the atmosphere driven by anthropogenic processes, and mediates a storage of CO2 in the ocean interior without which atmospheric CO2 would be much larger than it is today. Yet most of the material exported from the photic zone does not penetrate the deep ocean, instead it is mineralised in the twilight zone with fluxes in the thin 100m thick layer under the photic zone being extremely rapidly attenuated. The shape of this attenuation varies in time and space yet appears to be a critical determinand over atmosphere - ocean CO2 partitioning. Attempts to predict this attenuation using independent measures of heterotrophic activity have often not yielded the observed pattern of attenuation implying substantial uncertainties in one or more of the terms that enter into the comparison. In this talk we will describe direct estimates of particle flux made using drifting neutrally buoyant traps at the PAP site in 2009. We show that although we can make substantial progress towards closing the mid water C budget we still have a significant excess of carbon consumption over supply. We believe that this is due to erroneous steadystate assumptions, a hypothesis we explore via simple numerical models.

We analyze a model for CO oxidation on surfaces which incorporates both rapid diffusion of adsorbed CO, and superlattice ordering of adsorbed immobile oxygen on a square lattice of adsorption sites. The superlattice ordering derives from an {open_quotes}eight-site adsorption rule,{close_quotes} wherein diatomic oxygen adsorbs dissociatively on diagonally adjacent empty sites, provided that none of the six additional neighboring sites are occupied by oxygen. A {open_quotes}hybrid{close_quotes} formalism is applied to implement the model. Highly mobile adsorbed CO is assumed randomly distributed on sites not occupied by oxygen (which is justified if one neglects CO{endash}CO and CO{endash}O adspecies interactions), and is thus treated within a mean-field framework. In contrast, the distribution of immobile adsorbed oxygen is treated within a lattice{endash}gas framework. Exact master equations are presented for the model, together with some {ital exact} relationships for the coverages and reaction rate. A precise description of steady-state bifurcation behavior is provided utilizing both conventional and {open_quotes}constant-coverage ensemble{close_quotes} Monte Carlo simulations. This behavior is compared with predictions of a suitable analytic pair approximation derived from the master equations. The model exhibits the expected bistability, i.e., coexistence of highly reactive and relatively inactive states, which disappears at a cusp bifurcation. In addition, we show that the oxygen superlattice ordering produces a symmetry-breaking transition, and associated coarsening phenomena, not present in conventional Ziff{endash}Gulari{endash}Barshad-type reaction models. {copyright} {ital 1999 American Institute of Physics.}

We developed a Microbial-ENzyme-mediated Decomposition (MEND) model, based on the Michaelis-Menten kinetics, that describes the dynamics of physically defined pools of soil organic matter (SOC). These include particulate, mineral-associated, dissolved organic matter (POC, MOC, and DOC, respectively), microbial biomass, and associated exoenzymes. The ranges and/or distributions of parameters were determined by both analytical steady-state and dynamic analyses with SOC data from the literature. We used an improved multi-objective parameter sensitivity analysis (MOPSA) to identify the most important parameters for the full model: maintenance of microbial biomass, turnover and synthesis of enzymes, and carbon use efficiency (CUE). The model predicted an increase of 2 C (baseline temperature =12 C) caused the pools of POC-Cellulose, MOC, and total SOC to increase with dynamic CUE and decrease with constant CUE, as indicated by the 50% confidence intervals. Regardless of dynamic or constant CUE, the pool sizes of POC, MOC, and total SOC varied from 8% to 8% under +2 C. The scenario analysis using a single parameter set indicates that higher temperature with dynamic CUE might result in greater net increases in both POC-Cellulose and MOC pools. Different dynamics of various SOC pools reflected the catalytic functions of specific enzymes targeting specific substrates and the interactions between microbes, enzymes, and SOC. With the feasible parameter values estimated in this study, models incorporating fundamental principles of microbial-enzyme dynamics can lead to simulation results qualitatively different from traditional models with fast/slow/passive pools.

This paper documents a technique for deriving a steady-state, lumped-parameter model for capacitor-run, single-phase induction motors. The objective of this model is to predict motor performance parameters such as torque, loss distribution, and efficiency as a function of applied voltage and motor speed as well as the temperatures of the stator windings and of the rotor. The model includes representations of both the main and auxiliary windings (including arbitrary external impedances) and also the effects of core and rotational losses. The technique can be easily implemented and the resultant model can be used in a wide variety of analyses to investigate motor performance as a function of load, speed, and winding and rotor temperatures. The technique is based upon a coupled-circuit representation of the induction motor. A notable feature of the model is the technique used for representing core loss. In equivalent-circuit representations of transformers and induction motors, core loss is typically represented by a core-loss resistance in shunt with the magnetizing inductance. In order to maintain the coupled-circuit viewpoint adopted in this paper, this technique was modified slightly; core loss is represented by a set of core-loss resistances connected to the ``secondaries`` of a set of windings which perfectly couple to the air-gap flux of the motor. An example of the technique is presented based upon a 3.5 kW, single-phase, capacitor-run motor and the validity of the technique is demonstrated by comparing predicted and measured motor performance.

The constraint-based reconstruction and analysis (COBRA) framework has been widely used to study steady-state flux solutions in genome-scale metabolic networks. One shortcoming of current COBRA methods is the possible violation of the loop law in the computed steady-state flux solutions. The loop law is analogous to Kirchhoff's second law for electric circuits, and states that at steadystate there can be no net flux around a closed network cycle. Although the consequences of the loop law have been known for years, it has been computationally difficult to work with. Therefore, the resulting loop-law constraints have been overlooked. Here, we present a general mixed integer programming approach called loopless COBRA (ll-COBRA), which can be used to eliminate all steady-state flux solutions that are incompatible with the loop law. We apply this approach to improve flux predictions on three common COBRA methods: flux balance analysis, flux variability analysis, and Monte Carlo sampling of the flux space. Moreover, we demonstrate that the imposition of loop-law constraints with ll-COBRA improves the consistency of simulation results with experimental data. This method provides an additional constraint for many COBRA methods, enabling the acquisition of more realistic simulation results. PMID:21281568

Non-steady-state (NSS) chambers are widely used to measure trace gas emissions from the Earth’s surface in the atmosphere. Unfortunately, traditional interpretations of time-dependent chamber concentrations often systematically underestimate predeployment exchange rates because they do not accuratel...

One-dimensional mathematical models were developed for organic contaminant transport through landfill composite liners consisting of a geomembrane (GM) and a geosynthetic clay liner (GCL) or a GM and a compacted clay liner (CCL). The combined effect of leakage through GM defects, diffusion in GM and the underlying soil liners, and degradation in soil liners were considered. Steadystate analytical solutions were provided for the proposed mathematical models, which consider the different combinations of advection, diffusion, and degradation. The analytical solutions of the time lag for contaminant transport in the composite liners were also derived. The performance of GM/GCL and GM/CCL was analyzed. For GM/GCL, the bottom flux can be reduced by a factor of 4 when the leachate head decreases from 10 to 0.3 m. The influence of degradation can be ignored for GM/GCL. For GM/CCL, when the leachate head decreases from 10 to 0.3 m, the bottom flux decreases by a factor of 2-4. Leachate head has greater influence on bottom flux in case of larger degradation rate (e.g., half-life = 1 year) compared to the case with lower degradation rate (e.g., half-life = 10 years). As contaminant half-life in soil liner decreases from 10 to 1 year, bottom flux decreases by approximately 2.7 magnitudes of orders. It is indicated that degradation may have greater influence on time lag of composite liner than leachate head. As leachate head increases from zero to 10 m, time lag for GM/CCL can be reduced by 5-6 years. Time lag for the same composite liner can be reduced by 10-11 years as contaminant half-life decreases from 10 to 1 year. Reducing leachate head acting on composite liners and increasing the degradation capacity of the soil liner would be the effective methods to improve the performance of the composite liners. The proposed analytical solutions are relatively simple and can be used for preliminary design and performance assessment of composite liners. PMID:25893615

The model-independent estimation of physiological steady-state volume of distribution ([Formula: see text]), often referred to non-compartmental analysis (NCA), is historically based on the linear compartment model structure with central elimination. However the NCA-based steady-state volume of distribution ([Formula: see text]) cannot be generalized to more complex models. In the current paper, two-compartment models with simultaneous first-order and Michaelis-Menten elimination are considered. In particular, two indistinguishable models [Formula: see text] and [Formula: see text], both having central Michaelis-Menten elimination, while first-order elimination exclusively either from central or peripheral compartment, are studied. The model-based expressions of the steady-state volumes of distribution [Formula: see text] and their relationships to NCA-based [Formula: see text] are derived. The impact of non-linearity and peripheral elimination is explicitly delineated in the formulas. Being concerned with model identifiability and indistinguishability issues, an interval estimate of [Formula: see text] is suggested. PMID:27405818

The steadystate solution topology for absorption line-driven flows is investigated for the condition that the Sobolev approximation is not used to compute the line force. The solution topology near the sonic point is of the nodal type with two positive slope solutions. The shallower of these slopes applies to reasonable lower boundary conditions and realistic ion thermal speed v(th) and to the Sobolev limit of zero of the usual Castor, Abbott, and Klein model. At finite v(th), this solution consists of a family of very similar solutions converging on the sonic point. It is concluded that a non-Sobolev, absorption line-driven flow with a realistic values of v(th) has no uniquely defined steadystate. To the extent that a pure absorption model of the outflow of stellar winds is applicable, radiatively driven winds should be intrinsically variable.

Parameters in numerical ground-water flow models have been successfully estimated using nonlinear-optimization methods such as the modified Gauss-Newton (GN) method and conjugate-direction methods. This paper investigates the relative efficiency of GN and three conjugate-direction parameter-estimation methods on two-dimensional, steady-state and transient ground-water flow test cases. The steady-state test cases are included to compare the performance of the algorithm with published examples. The three conjugate-direction methods are the Fletcher-Reeves (FR) and quasi-Newton (QN) regression methods, and combination Fletcher-Reeves quasi-Newton (FR-QN). All three are combined with Newton's method of calculating step size. The numerical ground-water flow model is described by McDonald and Harbaugh.

SLAB-LLNL is a steady-state one-dimensional program which calculates the atmospheric dispersion of a heavier than air gas that is continuously released at ground level. The model is based on the steady-state crosswind-averaged conservation equations of species, mass, energy, and momentum. It uses the air entrainment concept to account for the turbulent mixing of the gas cloud with the surrounding atmosphere and similarity profiles to determine the crosswind dependence.

The purpose of this investigation was to develop a noise annoyance model, superior to those already in use, for evaluating passenger response to sounds containing tonal components which may be heard within current and future commercial aircraft. The sound spectra investigated ranged from those being experienced by passengers on board turbofan powered aircraft now in service to those cabin noise spectra passengers may experience within advanced propeller-driven aircraft of the future. A total of 240 sounds were tested in this experiment. Sixty-six of these 240 sounds were steadystate, while the other 174 varied temporally due to tonal beating. Here, the entire experiment is described, but the analysis is limited to those responses elicited by the 66 steady-state sounds.

Dynamic modeling and analysis of solid oxide fuel cell systems can provide insight towards meeting transient response application requirements and enabling an expansion of the operating envelope of these high temperature systems. SOFC modeling for system studies are accomplished with channel-level interface charge transfer models, which implement dynamic conservation equations coupled with additional submodels to capture the porous media mass transport and electrochemistry of the cell. Many of these models may contain simplifications in order to decouple the mass transport, fuel reforming, and electrochemical processes enabling the use of a 1-Dmodel. The reforming reactions distort concentration profiles of the species within the anode, where hydrogen concentration at the triple-phase boundary may be higher or lower than that of the channel altering the local Nernst potential and exchange current density. In part one of this paper series, the modeling equations for the 1-D and 'quasi' 2-D models are presented, and verified against button cell electrochemical and channel-level reforming data. Steady-state channel-level modeling results indicate a 'quasi' 2-D SOFC model predicts a more uniform temperature distribution where differences in the peak cell temperature and maximum temperature gradient are experienced. The differences are most prominent for counter-flow cell with high levels of internal reforming. The transient modeling comparison is discussed in part two of this paper series.

Volcanoes exhibit a wide range of eruption styles, from relatively slow effusive eruptions, generating lava flows and lava domes, to explosive eruptions, in which very large volumes of fragmented magma and volcanic gas are ejected high into the atmosphere. Magma ascent dynamics in a volcanic conduit play a key role in determining the eruptive style of a volcano. However, due to the lack of direct observations in the conduit itself, numerical models, constrained with observational data, provide invaluable tools for quantitative insights into the complex magma ascent processes. We have developed a 1Dsteady-state multiphase multicomponent gas-magma-solid mathematical model, consisting of a set of non-linear partial differential and constitutive equations. The governing equations used in this work are designed to model multiphase fluid with disequilibrium processes, represented through the formalism of thermodynamically compatible hyperbolic systems as a system of conservative partial differential equations with relaxation terms. This numerical model has been used to reproduce the 2001 flank eruption at mount Etna. During this eruption, seven fissures at different altitude were active, showing different eruptive styles: fire fountains, Strombolian activities and lava effusions. From a mineralogical point of view, two different lavas were erupted. The vent higher than 2600 m a.s.l. (hereafter Upper vents, UV) erupted plagioclase-rich magma with an high crystal content. On the other hand, the vents located at 2550 and 2100 m a.s.l. (hereafter Lower vents, LV) produced a plagioclase-poor magma with a lower crystal content than UV magmas. With our numerical model we have investigated both eruptive events at UV and LV. Using the estimation for volume flow rate and for crystal content we are able to constraint the conduit radius and the temperature of the magma chamber. Furthermore, our numerical results indicate that UV and LV magmas are originated from the same magma, but

Among all the algorithms to solve the wheel-rail contact problem, Kalker's FastSim has become the most useful computation tool since it combines a low computational cost and enough precision for most of the typical railway dynamics problems. However, some types of dynamic problems require the use of a non-steadystate analysis. Alonso and Giménez developed a non-stationary method based on FastSim, which provides both, sufficiently accurate results and a low computational cost. However, it presents some limitations; the method is developed for one time-dependent creepage and its accuracy for varying normal forces has not been checked. This article presents the required changes in order to deal with both problems and compares its results with those given by Kalker's Variational Method for rolling contact.

We have developed and tested two EEG-based brain-computer interfaces (BCI) for users to control a cursor on a computer display. Our system uses an adaptive algorithm, based on kernel partial least squares classification (KPLS), to associate patterns in multichannel EEG frequency spectra with cursor controls. Our first BCI, Target Practice, is a system for one-dimensional device control, in which participants use biofeedback to learn voluntary control of their EEG spectra. Target Practice uses a KF LS classifier to map power spectra of 30-electrode EEG signals to rightward or leftward position of a moving cursor on a computer display. Three subjects learned to control motion of a cursor on a video display in multiple blocks of 60 trials over periods of up to six weeks. The best subject s average skill in correct selection of the cursor direction grew from 58% to 88% after 13 training sessions. Target Practice also implements online control of two artifact sources: a) removal of ocular artifact by linear subtraction of wavelet-smoothed vertical and horizontal EOG signals, b) control of muscle artifact by inhibition of BCI training during periods of relatively high power in the 40-64 Hz band. The second BCI, Think Pointer, is a system for two-dimensional cursor control. Steady-state visual evoked potentials (SSVEP) are triggered by four flickering checkerboard stimuli located in narrow strips at each edge of the display. The user attends to one of the four beacons to initiate motion in the desired direction. The SSVEP signals are recorded from eight electrodes located over the occipital region. A KPLS classifier is individually calibrated to map multichannel frequency bands of the SSVEP signals to right-left or up-down motion of a cursor on a computer display. The display stops moving when the user attends to a central fixation point. As for Target Practice, Think Pointer also implements wavelet-based online removal of ocular artifact; however, in Think Pointer muscle

A 2D cellular automaton model has been developed to study the steady-state free'' growth of a non-isothermal dendrite. The model incorporates rules to account for heat diffusion, the influence of curvature on the equilibrium freezing temperature and latent heat evolution. The model predicts a V [proportional to] [Delta]T[sup b] growth rate-undercooling relationship for the various dendrite tip growth temperatures selected. The prediction of the values of b accords reasonably with analytical models and reported experimental observations.

Background In a previous study (Vaghefi et al. 2012) we described a 3D computer model that used finite element modeling to capture the structure and function of the ocular lens. This model accurately predicted the steadystate properties of the lens including the circulating ionic and fluid fluxes that are believed to underpin the lens internal microcirculation system. In the absence of a blood supply, this system brings nutrients to the core of the lens and removes waste products faster than would be achieved by passive diffusion alone. Here we test the predictive properties of our model by investigating whether it can accurately mimic the experimentally measured changes to lens steady-state properties induced by either depolarising the lens potential or reducing Na+ pump rate. Methods To mimic experimental manipulations reported in the literature, the boundary conditions of the model were progressively altered and the model resolved for each new set of conditions. Depolarisation of lens potential was implemented by increasing the extracellular [K+], while inhibition of the Na+ pump was stimulated by utilising the inherent temperature sensitivity of the pump and changing the temperature at which the model was solved. Results Our model correctly predicted that increasing extracellular [K+] depolarizes the lens potential, reducing and then reversing the magnitude of net current densities around the lens. While lowering the temperature reduced Na+ pump activity and caused a reduction in circulating current, it had a minimal effect on the lens potential, a result consistent with published experimental data. Conclusion We have shown that our model is capable of accurately simulating the effects of two known experimental manipulations on lens steady-state properties. Our results suggest that the model will be a valuable predictive tool to support ongoing studies of lens structure and function. PMID:23988187

This paper continues the series of numerical investigations of self-ionizing gas flows in plasma accelerator channels with an azimuthal magnetic field. The mathematical model is based on the equations of dynamics of a three-component continuous medium consisting of atoms, ions, and electrons; the model is supplemented with the equation of ionization and recombination kinetics within the diffusion approximation with account for photoionization and photorecombination. It also takes into account heat exchange, which in this case is caused by radiative heat conductance. Upon a short history of the issue, the proposed model, numerical methods, and results for steady-state and pulsating flows are described.

Steady-statemodels are useful for design of wastewater treatment plants (WWTPs) because they allow reactor sizes and interconnecting flows to be simply determined from explicit equations in terms of unit operation performance criteria. Once the overall WWTP scheme is established and the main system defining parameters of the individual unit operations estimated, dynamic models can be applied to the connected unit operations to refine their design and evaluate their performance under dynamic flow and load conditions. To model anaerobic digestion (AD) within plant-wide WWTP models, not only COD and nitrogen (N) but also carbon (C) fluxes entering the AD need to be defined. Current plant-wide models, like benchmark simulation model No 2 (BSM2), impose a C flux at the AD influent. In this paper, the COD and N mass balance steady-statemodels of activated sludge (AS) organics degradation, nitrification and denitrification (ND) and anaerobic (AD) and aerobic (AerD) digestion of wastewater sludge are extended and linked with bioprocess transformation stoichiometry to form C, H, O, N, chemical oxygen demand (COD) and charge mass balance based models so that also C (and H and O) can be tracked through the whole WWTP. By assigning a stoichiometric composition (x, y, z and a in C(x)H(y)O(z)N(a)) to each of the five main influent wastewater organic fractions and ammonia, these, and the products generated from them via the biological processes, are tracked through the WWTP. The model is applied to two theoretical case study WWTPs treating the same raw wastewater (WW) to the same final sludge residual biodegradable COD. It is demonstrated that much useful information can be generated with the relatively simple steady-statemodels to aid WWTP layout design and track the different products exiting the WWTP via the solid, liquid and gas streams, such as aerobic versus anaerobic digestion of waste activated sludge, N loads in recycle streams, methane production for energy recovery

Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by dislocation creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D dislocation dynamics (DD) model, which combines dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by dislocation creep in the lithospheric mantle at stresses <500 MPa. For stresses of 50-200 MPa, steady-state strain-rates of 10-15 s-1 may be attained at temperatures as low as 900 K. Fitting of the DD model produces a flow law, which represents a lower bound for the lithospheric mantle strength, since the models describe the deformation of an olivine single crystal in an easy slip orientation. Comparison of strain-rates and Moho temperatures inferred for different geodynamic environments and the predictions of this model-based flow law implies, nevertheless, that, except in incipient rifts, most of the observed deformation may be produced by stress levels ≤200 MPa, consistent with those inferred to be produced by convection. This convergence suggests that the present models, which explicitly calculate the time-dependent dislocation dynamics, may provide a correct first order estimate of the mechanical behaviour of the lithospheric mantle, which cannot be derived directly from any existing data.

The increase in steady-state force after active lengthening in skeletal muscle, termed force enhancement (FE), has been observed for nearly one century. Although demonstrated experimentally at various structural levels, the underlying mechanism(s) remain unknown. We recently showed that the Drosophila jump muscle is an ideal model for investigating mechanisms behind muscle physiological properties, because its mechanical characteristics, tested thus far, duplicate those of fast mammalian skeletal muscles, and Drosophila has the advantage that it can be more easily genetically modified. To determine if Drosophila would be appropriate to investigate FE, we performed classic FE experiments on this muscle. Steady-state FE (FESS), following active lengthening, increased by 3, 7, and 12% of maximum isometric force, with increasing stretch amplitudes of 5, 10, and 20% of optimal fiber length (FLOPT), yet was similar for stretches across increasing stretch velocities of 4, 20, and 200% FLOPT/s. These FESS characteristics of the Drosophila jump muscle closely mimic those observed previously. Jump muscles also displayed typical transient FE characteristics. The transient force relaxation following active stretch was fit with a double exponential, yielding two phases of force relaxation: a fast initial relaxation of force, followed by a slower recovery toward steadystate. Our analyses identified a negative correlation between the slow relaxation rate and FESS, indicating that there is likely an active component contributing to FE, in addition to a passive component. Herein, we have established the Drosophila jump muscle as a new and genetically powerful experimental model to investigate the underlying mechanism(s) of FE. PMID:26289752

A method to calculate the response on the surface of a multilayered half-space for a fault of finite width and infinite length is presented. The model involves a piecewise-rectilinear and continuous rupture front propagating at a constant rupture velocity along the length of a fault of arbitrary dip angle. The motion produced by this steadystate dislocation model corresponds to the passage of the rupture front phase, which is a predominant phase in the near-source region away from the ends of a finite fault. The model gives an efficient way to synthesize a ubiquitous, intermediate frequency, high-amplitude pulse observed in many near-source records. A series of validation tests, using both three- and two-dimensional kinematic fault models, and a limited set of parametric studies clarifying the mechanisms involved in the generation of high amplitudes, are presented. Finally, it is shown that the distribution of peak horizontal velocities in the near-source region calculated by use of a steadystatemodel in a layered medium compare favorably with the regression results of Joyner and Boore (1981).

This paper shows that semi-empirical data-driven models based on a two-time-scale approximation for the magnetic and kinetic control of advanced tokamak (AT) scenarios can be advantageously identified from simulated rather than real data, and used for control design. The method is applied to the combined control of the safety factor profile, q(x), and normalized pressure parameter, βN, using DIII-D parameters and actuators (on-axis co-current neutral beam injection (NBI) power, off-axis co-current NBI power, electron cyclotron current drive power, and ohmic coil). The approximate plasma response model was identified from simulated open-loop data obtained using a rapidly converging plasma transport code, METIS, which includes an MHD equilibrium and current diffusion solver, and combines plasma transport nonlinearity with 0D scaling laws and 1.5D ordinary differential equations. The paper discusses the results of closed-loop METIS simulations, using the near-optimal ARTAEMIS control algorithm (Moreau D et al 2013 Nucl. Fusion 53 063020) for steadystate AT operation. With feedforward plus feedback control, the steadystate target q-profile and βN are satisfactorily tracked with a time scale of about 10 s, despite large disturbances applied to the feedforward powers and plasma parameters. The robustness of the control algorithm with respect to disturbances of the H&CD actuators and of plasma parameters such as the H-factor, plasma density and effective charge, is also shown.

The combined use of a gas-exchange system and laser-based isotope measurement is a tool of growing interest in plant ecophysiological studies, owing to its relevance for assessing isotopic variability in leaf water and/or transpiration under non-steady-state (NSS) conditions. However, the current Farquhar & Cernusak (F&C) NSS leaf water model, originally developed for open-field scenarios, is unsuited for use in a gas-exchange cuvette environment where isotope composition of water vapour (δv ) is intrinsically linked to that of transpiration (δE ). Here, we modified the F&C model to make it directly compatible with the δv -δE dynamic characteristic of a typical cuvette setting. The resultant new model suggests a role of 'net-flux' (rather than 'gross-flux' as suggested by the original F&C model)-based leaf water turnover rate in controlling the time constant (τ) for the approach to steady sate. The validity of the new model was subsequently confirmed in a cuvette experiment involving cotton leaves, for which we demonstrated close agreement between τ values predicted from the model and those measured from NSS variations in isotope enrichment of transpiration. Hence, we recommend that our new model be incorporated into future isotope studies involving a cuvette condition where the transpiration flux directly influences δv . There is an increasing popularity among plant ecophysiologists to use a gas-exchange system coupled to laser-based isotope measurement for investigating non-steadystate (NSS) isotopic variability in leaf water (and/or transpiration); however, the current Farquhar & Cernusak (F&C) NSS leaf water model is unsuited for use in a gas-exchange cuvette environment due to its implicit assumption of isotope composition of water vapor (δv ) being constant and independent of that of transpiration (δE ). In the present study, we modified the F&C model to make it compatible with the dynamic relationship between δv and δE as is typically associated

We have developed an atomistic lattice-gas model for the catalytic oxidation of CO on single-crystal Pd(100) surfaces under ultrahigh vacuum conditions. This model necessarily incorporates an detailed description of adlayer ordering and adsorption-desorption kinetics both for CO on Pd(100), and for oxygen on Pd(100). Relevant energetic parameters are determined by comparing model predictions with experiment, together with some guidance from density functional theory calculations. The latter also facilitates description of the interaction and reaction of adsorbed CO and oxygen. Kinetic Monte Carlo simulations of this reaction model are performed to predict temperature-programmed reaction spectra, as well as steady-state bifurcation behavior. PMID:16674249

A class of steady-state compartmental models of the circulation is examined and it is shown that the mathematical problem for this model class involves a single nonlinear equation. In an important subclass and with certain assumptions regarding the form of the Starling-type cardiac function curves, the single equation is of the form Z = μ + λ log[(1 - Z)/Z] where μ and λ are mathematical parameters related to the physiological parameters of the system and Z is proportional to the cardiac output. This result holds regardless of the number and arrangement of compartments within the model itself or of the number of physiological parameters the model contains. An example of this class with 25 physiological parameters is presented to illustrate this approach. PMID:27587712

Sediment biogeochemical processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be an important driver of bottom water oxygen depletion in hypoxic systems, and sediment-water nutrient fluxes support primary productivity in the overlying water column. Yet, biogeochemical sediment-water fluxes are often parameterized crudely and only poorly constrained in coupled physical-biogeochemical models. Here, we present a method for parameterizing biogeochemical sediment-water fluxes realistically and efficiently, using in-situ measurements and a steadystate diagenetic model. We apply this method to the Louisiana Shelf where high primary production induced by excess nutrient loads from the Mississippi-Atchafalaya River system promotes the development of hypoxic bottom waters in summer. The implementation of the parameterizations in a coupled circulation-biogeochemical model of the northern Gulf of Mexico results in realistic sediment-water fluxes that enable a sediment-water column feedback at low bottom oxygen concentrations.

The ability of groundwater models to inform recharge through calibration is hampered by the correlation between recharge and aquifer parameters such as hydraulic conductivity (K), and the insufficient information content of observation datasets. These factors collectively result in non-uniqueness of parameter estimates. Previous studies that jointly estimate spatially distributed recharge and hydraulic parameters are limited to synthetic test cases and/or do not evaluate the effect of non-uniqueness. The extent to which recharge can be informed by calibration is largely unknown for practical situations, in which complexities such as parameter heterogeneities are inherent. In this study, a systematic investigation of recharge, inferred through model calibration, is undertaken using a series of numerical experiments that include varying degrees of hydraulic parameter information. The analysis involves the use of a synthetic reality, based on a regional-scale, highly parameterised, steady-state groundwater model of Uley South Basin, South Australia. Parameter identifiability is assessed to evaluate the ability of parameters to be estimated uniquely. Results show that a reasonable inference of recharge (average recharge error <10%) requires a surprisingly large number of preferred value regularisation constraints (>100 K values across the 129 km2 study area). The introduction of pumping data into the calibration reduces error in both the average recharge and its spatial variability, whereas submarine groundwater discharge (as a calibration target) reduces average recharge error only. Nonetheless, the estimation of steady-state recharge through inverse modelling may be impractical for real-world settings, limited by the need for unrealistic amounts of hydraulic parameter and groundwater level data. This study provides a useful benchmark for evaluating the extent to which field-scale groundwater models can be used to inform recharge subject to practical data

The development, implementation and flight test evaluation of a performance modeling technique which required a limited amount of quasisteady state flight test data to predict the overall one g performance characteristics of an aircraft. The concept definition phase of the program include development of: (1) the relationship for defining aerodynamic characteristics from quasi steadystate maneuvers; (2) a simplified in flight thrust and airflow prediction technique; (3) a flight test maneuvering sequence which efficiently provided definition of baseline aerodynamic and engine characteristics including power effects on lift and drag; and (4) the algorithms necessary for cruise and flight trajectory predictions. Implementation of the concept include design of the overall flight test data flow, definition of instrumentation system and ground test requirements, development and verification of all applicable software and consolidation of the overall requirements in a flight test plan.

A variety of chemical equilibrium models have been developed to help assess environmental chemistry problems, but few were specifically developed as research and teaching tools for use in conjunction with soil chemistry experiments. MANE model was developed to calculate equilibri...

Examples of potential use of the model to investigate the groundwater system include (1) the effects of different recharge, (2) different interpretations of the extent or offset of long faults or fault zones, and (3) different conceptual models of the spatial variation of hydraulic properties. The model can also be used to examine the ultimate effects of groundwater withdrawals on a regional scale, to provide boundary conditions for local-scale models, and to guide data collection.

Perhaps the most mature area of multi-scale systems biology is the modelling of the heart. Current models are grounded in over fifty years of research in the development of biophysically detailed models of the electrophysiology (EP) of cardiac cells, but one aspect which is inadequately addressed is the incorporation of uncertainty and physiological variability. Uncertainty quantification (UQ) is the identification and characterisation of the uncertainty in model parameters derived from experimental data, and the computation of the resultant uncertainty in model outputs. It is a necessary tool for establishing the credibility of computational models, and will likely be expected of EP models for future safety-critical clinical applications. The focus of this paper is formal UQ of one major sub-component of cardiac EP models, the steady-state inactivation of the fast sodium current, INa. To better capture average behaviour and quantify variability across cells, we have applied for the first time an ‘individual-based’ statistical methodology to assess voltage clamp data. Advantages of this approach over a more traditional ‘population-averaged’ approach are highlighted. The method was used to characterise variability amongst cells isolated from canine epi and endocardium, and this variability was then ‘propagated forward’ through a canine model to determine the resultant uncertainty in model predictions at different scales, such as of upstroke velocity and spiral wave dynamics. Statistically significant differences between epi and endocardial cells (greater half-inactivation and less steep slope of steadystate inactivation curve for endo) was observed, and the forward propagation revealed a lack of robustness of the model to underlying variability, but also surprising robustness to variability at the tissue scale. Overall, the methodology can be used to: (i) better analyse voltage clamp data; (ii) characterise underlying population variability; (iii

Perhaps the most mature area of multi-scale systems biology is the modelling of the heart. Current models are grounded in over fifty years of research in the development of biophysically detailed models of the electrophysiology (EP) of cardiac cells, but one aspect which is inadequately addressed is the incorporation of uncertainty and physiological variability. Uncertainty quantification (UQ) is the identification and characterisation of the uncertainty in model parameters derived from experimental data, and the computation of the resultant uncertainty in model outputs. It is a necessary tool for establishing the credibility of computational models, and will likely be expected of EP models for future safety-critical clinical applications. The focus of this paper is formal UQ of one major sub-component of cardiac EP models, the steady-state inactivation of the fast sodium current, INa. To better capture average behaviour and quantify variability across cells, we have applied for the first time an 'individual-based' statistical methodology to assess voltage clamp data. Advantages of this approach over a more traditional 'population-averaged' approach are highlighted. The method was used to characterise variability amongst cells isolated from canine epi and endocardium, and this variability was then 'propagated forward' through a canine model to determine the resultant uncertainty in model predictions at different scales, such as of upstroke velocity and spiral wave dynamics. Statistically significant differences between epi and endocardial cells (greater half-inactivation and less steep slope of steadystate inactivation curve for endo) was observed, and the forward propagation revealed a lack of robustness of the model to underlying variability, but also surprising robustness to variability at the tissue scale. Overall, the methodology can be used to: (i) better analyse voltage clamp data; (ii) characterise underlying population variability; (iii) investigate

Grace and McLean (2006) proposed a decision model for acquisition of choice in concurrent chains which assumes that after reinforcement in a terminal link, subjects make a discrimination whether the preceding reinforcer delay was short or long relative to a criterion. Their model was subsequently extended by Christensen and Grace (2008, 2009a,…

Activated sludge treatment of a xenobiotic organic compound, much different from treatment of biogenic organics, must be modeled with interactions involving a two-part biomass of degrader and nondegrader, which selectively or competitively grow on a two-part substrate of input xenobiotic and its biogenic metabolites. A xenobiotic treatment model was developed which incorporates kinetics of the growth of degrader and nondegrader, the line dividing metabolites into xenobiotic and biogenic, yields of degrader and nondegrader from utilization of their parts of substrates, and kinetics of degrader reversion to nondegrader due to instability of the degradative element degraders carry. Experimental activated sludge operated for treatment of a xenobiotic generated data for calibration of the model. With the input of influent xenobiotic concentration, mean cell and hydraulic residence times, and calibrated parameters, the model readily outputs concentrations of degrader, nondegrader, and effluent biogenic residue that closely match the results obtained from experiments. PMID:25561268

The elimination of Ampholine from the system by establishing the pH gradient with simple ampholytes is proposed. A mathematical model was exercised at the level of the two-component system by using values for mobilities, diffusion coefficients, and dissociation constants representative of glutamic acid and histidine. The constants assumed in the calculations are reported. The predictions of the model and computer simulation of isoelectric focusing experiments are in direct importance to obtain Ampholine-free, stable pH gradients.

The switched reluctance motor (SRM) has been a popular topic of research for the last 15 years. As a result of this development activity, the SRM has evolved into a practical alternative to other machines for a variety of applications. It is now becoming increasingly important to understand the SRM`s control characteristics and power requirements. To accomplish this a thorough description of the machine`s terminal characteristics is required. The SRM can be described as a system with two ports, the windings through which electrical power is transferred and the shaft through which mechanical power flows. These systems are coupled by a magnetic system, through which the energy conversion process occurs. The windings can be modelled as an inductor and much work has focused on the modelling of the SRM inductance. The difficulty with this approach is that the SRM magnetic structures must operate in deep saturation resulting in a nonlinear winding inductance. Many people have linearized this inductance using a variety of techniques but each results in unnecessarily complicated models for many applications. In this paper a relatively simple model for the SRM is developed. This type of model could be a cheap and effective tool for the development of SRM drive systems. This approach will become increasingly relevant as these drives become increasingly popular. In this paper the machine terminal characteristics in terms of flux linkage are described. It will be shown that flux linkage is a function of two variables resulting in a surface function. Additionally it will be shown that this surface function contains the terminal characteristics of the SRM. Finally measurements from actual hardware are made and used to develop a model using the techniques developed here. Results of model simulation are then compared with measured data.

The balance of stable and decaying tracers was incorporated into a latitude-depth ocean circulation model which resolves the major ocean basin and is coupled to an atmospheric energy balance model. The modern distribution of radiocarbon and the analysis of artificial color tracers enabled the census of the deep water masses. We show that good agreement with the observation can be achieved if the surface forcing is modified. The same process could also account for long-term, large-scale changes of the global thermohaline circulation. Uptake rates of carbon are investigated using an inorganic carbon cycle model and performing 2 [times] CO[sub 2]-experiments. We prescribe the industrial evolution of pCO[sub 2] in the atmosphere from 1792 to 1988 and calculate the total flux of carbon into the world ocean. Results are in good agreement with two recent 3-dimensional model simulation. First results using an organic carbon cycle in this model are presented. Changes in the hydrological cycle can stabilize the thermohaline circulation in the Atlantic and enable simulation of climate events resembling the Younger Dryas. By adding the balance of radiocarbon the evolution of its atmospheric concentration is studied during rapid changes of deep ocean ventilation. A resumption of ventilation creates a rapid decrease of atmospheric radiocarbon which is able to mask the natural decay.

The deep circulation model developed by Wright and Stocker has been used to represent the latitude-depth distributions of temperature, salinity, radiocarbon and color'' tracers in the Pacific, Atlantic and Indian Oceans. Restoring temperature and salinity to observed surface data the model shows a global thermohaline circulation where deep water is formed in the North Atlantic and in the Southern Ocean. A parameter study reveals that the high-latitude surface salinity determines the composition of deep water and its flow in the global ocean. Increasing Southern Ocean surface salinity by 0.4 ppt the circulation changes from a present-day mode where North Atlantic Deep Water is one where Antarctic Bottom Water is dominant. An inorganic carbon cycle with surface carbonate chemistry is included, and gas exchange is parameterized in terms of pCO{sub 2} differences. Pre- industrial conditions are achieved by adjusting the basin-mean alkalinity. A classical 2{times}CO{sub 2} experiment yields the intrinsic time scales for carbon uptake of the ocean; they agree with those obtained from simple box models or 3-dimensional ocean general circulation models. Using the estimated industrial anthropogenic input of CO{sub 2} into the atmosphere the model requires, consistent with other model studies, an additional carbon flux to match the observed increase of atmospheric pCO{sub 2}. We use more realistic surface boundary conditions which reduce sensitivity to freshwater discharges into the ocean. In a glacial-to-interglacial experiment rapid transitions of the deep circulation between two different states occur in conjunction with a severe reduction of the meridional heat flux and sea surface temperature during peak melting. After the melting the conveyor belt circulation restarts.

The primary objective was to present methods for validating predictions of Rocketdyne's most current version of the Space Shuttle Main Engine (SSME) Power Balance Model (PBM) with respect to physical relations governing flow systems. This required the development and implementation of postprocessors to check results of PBM computations for satisfaction of conservation relations. A cursory uncertainty analysis of PBM predictions with respect to mass and energy balances was performed. In addition, an effort to identify the empirical relations and physical assumptions within PBM which impact the ability of the model to attain rigorous balance was begun.

In many situations where annual crops are irrigated with saline water, root zone salinity does not reach a steadystate. Use of a steady-state description of root zone salinity may then seriously overestimate the calculated leaching requirements of the crop. A steady-state semi-emphirical model of crop response to irrigation with saline water has been calibrated using data from a number of field experiments. Predictions of yield deficit resulting from irrigation with saline water have been made for each of these experiments, using both the original model and a modified version which allows for the non-steady-state salinity conditions occurring in the experiments. Comparison with experimental data shows a clear superiority of the modified version in most cases studied. Where the original model is superior or equally good, it is likely that steady-state conditions are being approached. Where root zone salinity data were available and applicable, the modified model predicted root zone salinity much better. Approaches for distinguishing errors in calibration from intrinsic errors in the model assumptions are discussed.

We derive an analytical expression for entropy production in earthquake populations based on Dewar’s formulation, including flux (tectonic forcing) and source (earthquake population) terms, and apply it to the Olami-Feder-Christensen (OFC) numerical model for earthquake dynamics. Assuming the commonly-observed power-law rheology between driving stress and remote strain rate, we test the hypothesis that maximum entropy production (MEP) is a thermodynamic driver for self-organized ‘criticality’ (SOC) in the model. MEP occurs when the global elastic strain is near, but strictly sub-critical, with small relative fluctuations in macroscopic strain energy expressed by a low seismic efficiency, and broad-bandwidth power-law scaling of frequency and rupture area. These phenomena, all as observed in natural earthquake populations, are hallmarks of the broad conceptual definition of SOC, which to date has often in practice included self-organizing systems in a near but strictly sub-critical state. In contrast the precise critical point represents a state of minimum entropy production in the model. In the MEP state the strain field retains some memory of past events, expressed as coherent ‘domains’, implying a degree of predictability, albeit strongly limited in practice by the proximity to criticality, our inability to map the stress field at an equivalent resolution to the numerical model, and finite temporal sampling effects in real data.

The kinetics of aggregation for particles of various sizes depends on their diffusive arrival and fusion at a specific nucleation site. We present here a mean-field approximation and a stochastic jump model for aggregates at equilibrium. This approach is an alternative to the classical Smoluchowski equations that do not have a close form and are not solvable in general. We analyze these mean-field equations and obtain the kinetics of a cluster formation. Our approach provides a simplified theoretical framework to study the kinetics of viral capsid formation, such as HIV from the self-assembly of the structural proteins Gag.

A model of the biota sediment accumulation factor (BSAF) is developed to relate the ratio of metal concentrations in two marine bivalves (Crassostrea virginica and Mytilus edulis) to sediment metal concentration. A generalized metal BSAF can be approximated by a simple relationship that is a function of sediment to water column partitioning, the bioconcentration factor (BCF), the depuration rate, the metal assimilation efficiency from food, the bivalve feeding rate, and the growth rate. Analyses of Mussel Watch data indicate that the medium BSAF across stations varies by about three orders of magnitude from Zn, Cd, and Cu at the highest levels of BSAF = 1 to 10, while Cr has the lowest BSAF at 0.01. Total Hg is about 1.0 and Ni and Pb are approximately 0.1. Calibration of the model indicates that the food route of metal accumulation is significant for all metals but specially for Zn, Cd, Cu, and Hg where virtually all of the observed BSAF is calculated to be due to ingestion of metal from food in the overlying water. These results indicate a potential significance of the metal-binding protein metallothionein, which results in relatively high binding of metal and resulting low depuration rates.

Agricultural waste is one of the main renewable energy resources available, especially in an agricultural country such as Serbia. Pyrolysis has already been considered as an attractive alternative for disposal of agricultural waste, since the technique can convert this special biomass resource into granular charcoal, non-condensable gases and pyrolysis oils, which could furnish profitable energy and chemical products owing to their high calorific value. In this regard, the development of thermochemical processes requires a good understanding of pyrolysis mechanisms. Experimental and some literature data on the pyrolysis characteristics of corn cob and several other agricultural residues under inert atmosphere were structured and analysed in order to obtain conversion behaviour patterns of agricultural residues during pyrolysis within the temperature range from 300 °C to 1000 °C. Based on experimental and literature data analysis, empirical relationships were derived, including relations between the temperature of the process and yields of charcoal, tar and gas (CO2, CO, H2 and CH4). An analytical semi-empirical model was then used as a tool to analyse the general trends of biomass pyrolysis. Although this semi-empirical model needs further refinement before application to all types of biomass, its prediction capability was in good agreement with results obtained by the literature review. The compact representation could be used in other applications, to conveniently extrapolate and interpolate these results to other temperatures and biomass types. PMID:27281226

Ulysses observations of the high-latitude solar wind were combined with Spartan 201 observations of the corona to investigate the nature and extent of uncertainties in our knowledge of solar wind structure near the Sun. In addition to uncertainties stemming from the propagation of errors in density profiles inferred from coronagraph observations [see, e.g., {ital Lallement} {ital et al.}, 1986], an assessment of the consequences of choosing different analysis assumptions reveals very large, fundamental uncertainties in our knowledge of even the basics of coronal structure near the Sun. In the spirit of demonstrating the nature and extent of these uncertainties we develop just one of a generic class of explicitly time-dependent and filamentary models of the corona that is consistent with the Ulysses and Spartan 201 data. This model provides a natural explanation for the radial profiles of both the axial ratios and apparent radial speeds of density irregularities measured at radial distances less than 10R{sub S} using the interplanetary scintillation technique. {copyright} 1997 American Geophysical Union

In the aerobic biological treatment of wastewater, microorganisms use oxygen to decompose organic contaminants. Carbon dioxide, water and biosolids -- or sludge -- are the primary products. After a predetermined time in the reactor or aeration basin, the sludge is either removed from the process or sent to a clarifier, where it settles. Some of this sludge is recycled back to the aeration basin to initiate further oxidation, and some is removed from the process. In many aerobic processes, the average retention time of the sludge in the aeration basin -- called the sludge age -- is the main design parameter. However, other parameters, such as the rate of oxygen transfer rates and the capacity of the clarifier can affect the quality of the effluent. A simple mathematical model can be used to calculate these parameters.

We consider quantum quenches to the sinh-Gordon integrable quantum field theory from a particular class of initial states. Our analysis includes the case of mass and interaction quenches starting from a non-interacting theory. By means of the recently developed quench action method, we fully characterize the stationary state reached at long times after the quench in terms of the corresponding rapidity distribution. We also provide exact results for the expectation values of arbitrary vertex operators in the post-quench stationary state by proposing a formula based on the analogy with the standard thermodynamic Bethe ansatz. Finally, we comment on the behavior of the post-quench stationary state under the mapping between the sinh-Gordon field theory and the one-dimensional Lieb-Liniger model.

The fuel element for one of the many reactor concepts being currently evaluated for bimodal applications in space consists of spherical fuel particles clad with tungsten or alloys of tungsten. The fuel itself consists of stabilized UO{sub 2}. One of the life limiting phenomena for the fuel element is failure of the cladding because of creep deformation. This report summarizes the information available in literature regarding the creep deformation of tungsten and its alloys and proposes a relation to be used for calculating the creep strains for elevated temperatures in the low stress region ({sigma} {le} 20 MPa). Also, results of the application of this creep relation to one of the reactor design concepts (NEBA-3) are discussed. Based on the traditional definition of creep deformation, the temperatures of 1500 K to 2900 K for tungsten and its alloys are considered to be in the {open_quotes}high{close_quotes} temperature range. In this temperature range, the rate controlling mechanisms for creep deformation are believed to be non-conservative motion of screw dislocations and short circuit diffusional paths. Extensive theoretical work on creep and in particular for creep of tungsten and its alloys have been reported in the literature. These theoretical efforts have produced complex mathematical models that require detailed materials properties. These relations, however, are not presently suitable for the creep analysis because of lack of consistent material properties required for their use. Variations in material chemistry and thermomechanical pre-treatment of tungsten have significant effects on creep and the mechanical properties. Analysis of the theoretical models and limited data indicates that the following empirical relation originally proposed by M. Jacox of INEL and the Air Force Phillips Laboratory, for calculating creep deformation of tungsten cladding, can be used for the downselection of preliminary bimodal reactor design concepts.

Due to the diminishing availability of good quality water for irrigation, it is increasingly important that irrigation and salinity management tools be able to target submaximal crop yields and support the use of marginal quality waters. In this work, we present a steady-state irrigated systems modeling framework that accounts for reduced plant water uptake due to root zone salinity. Two new explicit, closed-form analytical solutions for the root zone solute concentration profile are obtained, corresponding to two alternative functional forms of the uptake reduction function. The solutions express a general relationship between irrigation water salinity, irrigation rate, crop salt tolerance, crop transpiration, and (using standard approximations) crop yield. Example applications are illustrated, including the calculation of irrigation requirements for obtaining targeted submaximal yields, and the generation of crop-water production functions for varying irrigation waters, irrigation rates, and crops. Model predictions are shown to be mostly consistent with existing models and available experimental data. Yet the new solutions possess clear advantages over available alternatives, including: (i) the new solutions were derived from a complete physical-mathematical description of the system, rather than based on an ad hoc formulation; (ii) the new analytical solutions are explicit and can be evaluated without iterative techniques; (iii) the solutions permit consideration of two common functional forms of salinity induced reductions in crop water uptake, rather than being tied to one particular representation; and (iv) the utilized modeling framework is compatible with leading transient-state numerical models.

Evaluation of performance of a BLSS model, including higher plants for food production and biodegradation of human waste, in long-term operation in dynamic and steadystates was performed. The model system was conceived for supplying vegetarian food and oxygen to 0.07 human. The following data were obtained in steady-state operating conditions. Average rate of wheat, chufa, radish, lettuce and Salicornia edible biomass accumulation were 8.7, 5.5, 0.6, 0.6 and metricconverterProductID2.5 g2.5 g per day respectively. Thus, to mimic the vegetarian edible biomass consumption by a human it was necessary to withdraw 17.9 g/d from total mass ex-change. Simultaneously, human mineralized exometabolites (artificial mineralized urine, AMU) in the amount of approximately 7% of a daily norm were introduced into the nutrient solu-tion for irrigation of the plants cultivated on a neutral substrate (expanded clay aggregate). The estimated value of 5.8 g/d of wheat and Salicornia inedible biomass was introduced in the soil-like substrate (SLS) to fully meet the plants need in nitrogen. The rest of wheat and Salicornia inedible biomass, 5.7 g/d, was stored. Thus in all, 23.6g of vegetarian dry matter had been stored. Assuming edible biomass is eaten up by the human, the closure coefficient of the vegetarian biomass inclusion into matter recycling amounted to 88%. The analysis of the long-term model operation showed that the main factors limiting increase of recycling processes were the following: a) Partly unbalanced mineral composition of daily human waste with daily needs of plants culti-` vated in the system. Thus, when fully satisfied with respect to nitrogen, the plants experienced a lack of macro elements such as P, Mg and Ca by more than 50%; b) Partly unbalanced mineral composition of edible biomass of the plants cultivated in the SLS with that of inedible biomass of the plants cultivated by hydroponic method on neutral substrate introduced in the SLS; c) Accumulation of

Steady-state boiling experiments were performed in the SBLB test facility to observe the two-phase boundary layer flow behavior on the outer surface of a heated hemispherical vessel near the critical heat flux (CHF) limit and to measure the spatial variation of the local CHF along the vessel outer surface. Based upon the flow observations, an advanced hydrodynamic CHF model was developed. The model considers the existence of a micro-layer underneath an elongated vapor slug on the downward facing curved heating surface. The micro-layer is treated as a thin liquid film with numerous micro-vapor jets penetrating through it. The micro-jets have the characteristic size dictated by Helmholtz instability. Local dryout is considered to occur when the supply of fresh liquid from the two phase boundary layer to the micro-layer is not sufficient to prevent depletion of the liquid film by boiling. A boundary layer analysis, treating the two-phase motion as a separated flow, is performed to determine the liquid supply rate and thus the local critical heat flux. The model provides a clear physical explanation for the spatial variation of the CHF observed in the SBLB experiments and for the weak dependence of the CHF data on the physical size of the vessel.

Gene translation is a central stage in the intracellular process of protein synthesis. Gene translation proceeds in three major stages: initiation, elongation, and termination. During the elongation step, ribosomes (intracellular macromolecules) link amino acids together in the order specified by messenger RNA (mRNA) molecules. The homogeneous ribosome flow model (HRFM) is a mathematical model of translation-elongation under the assumption of constant elongation rate along the mRNA sequence. The HRFM includes $(n)$ first-order nonlinear ordinary differential equations, where $(n)$ represents the length of the mRNA sequence, and two positive parameters: ribosomal initiation rate and the (constant) elongation rate. Here, we analyze the HRFM when $(n)$ goes to infinity and derive a simple expression for the steady-state protein synthesis rate. We also derive bounds that show that the behavior of the HRFM for finite, and relatively small, values of $(n)$ is already in good agreement with the closed-form result in the infinite-dimensional case. For example, for $(n=15)$, the relative error is already less than 4 percent. Our results can, thus, be used in practice for analyzing the behavior of finite-dimensional HRFMs that model translation. To demonstrate this, we apply our approach to estimate the mean initiation rate in M. musculus, finding it to be around 0.17 codons per second. PMID:24384716

We present a model of the steady-state transport assuming three reservoirs: a lower mantle (P) with a relatively undepleted inventory of U, Th, Pu, I, He, Ne, Xe, Ar; an upper mantle that has been extensively outgassed (D); and the atmosphere. There is mass transport at a rate M(sub PD) by plumes from the lower mantle, a fraction of which is outgassed directly into the atmosphere, while the remainder feeds matter and associated nuclei into D. D is well outgassed at spreading centers and has material containing atmospheric gases added to it by subduction. In the case of He, there is no subduction component. The approach follows the treatment of Kellogg and Wasserburg. A summary of the pertinent equations and constraints was reported earlier. The U, Th and Pu in P are estimated for Earth models from refractory element abundances in meteorites. In this model the inventory of rare gases in D is governed by the simple mixing of components from P (both radiogenic and original) with distinctive atmospheric components. In addition, alpha decay and spontaneous fission of U, and (alpha, n) reaction on oxygen from energetic alpha particles produce radiogenic/nuclear daughter products in D. These include (4)He, (136)Xe and (21)Ne. (40)K in D generates excess radiogenic (40)Ar.

This work describes a systematic experimental study and kinetic modelling of the steadystate and the transients associated with the turn-on and turn-off of a NO hollow cathode discharge. The local charge density and mean electron energy have been determined with a double Langmuir probe. Time-resolved Fourier transform infrared spectroscopy and electron bombardment quadrupole mass spectrometry with ionization by electron impact have been used to measure the gas temperature and the concentrations of the stable molecules present in the discharge: the precursor, NO, the major products, N2, O2, and the minor species NO2 and N2O. Emission spectroscopy has been employed to study the time behaviour of the very reactive nitrogen and oxygen atoms. A model based on a reduced set of kinetic equations including electron dissociation, gas-phase reactions, and gas-surface processes gives a global account of the measured data. From the time-resolved results, electron impact dissociation rate constants for some of the involved species under the conditions of the experiment are estimated. This model is compared with that obtained in previous works on N2O plasmas.

SummaryThe study of unconfined steady aquifer flow is usually based on either the numerical integration of the Laplace equation or on its analytical solution using the complex variable theory. A further approach that uses Adomian's method of decomposition yields simple analytical solutions in higher dimensions, does not require linearisation of the free-surface boundary condition and yields the elevation of the seepage face. A common approach is the introduction of simplified one-dimensional models that are often accurate enough for practical applications. However, the water table estimates derived by the so-called Dupuit-Forchheimer theory do not always fulfil the required accuracy. This work improves the Dupuit-Forcheimer hypotheses to obtain more precise results. For this purpose, the stream function of the groundwater flow net is formulated in natural, curvilinear coordinates. Next, an approximate one-dimensional model for the water table height is derived considering Darcy's law, retaining the curved features of the flow net. The proposed model is a higher order Dupuit-Forchheimer type approach, which was favourably compared with 2D results for Polubarinova-Kochina's rectangular dam problem and the drainage to symmetrically located ditches under steady-state conditions.

This article outlines the development of a steady-state thermal model for the pusher-type steel reheating furnace. Problems commonly encountered with this furnace type are skidmark generation, scale formation, and high energy consumption. The objective of the work is to provide a means by which furnace users might assess the effectiveness of changes to current operating practices, proposed furnace modifications, or new furnace designs in controlling these difficulties. The operation of the model, which develops the thermal history of an individual slab or billet as it passes through the furnace, is presented, and each of the three modules that comprise the model is described. Initial verification of the model has been carried out using data obtained in a separate campaign of plant trials on several 32-m furnace reheating slabs, and model predictions for steel temperatures at six locations within the steel are shown to be in good agreement with the experimental results. The model is used to examine the influence of two skid designs and several placement strategies on skidmark severity and energy losses to the skid system. Although skidmark severity at the intermediate stages of heating is shown to be dependent on both the skid type and the location of any offsets, it is demonstrated that the skidmark present in the discharged steel is determined primarily by the skid type employed over the final section of the furnace. The results suggest that, in the absence of a hearth section, the use of a well-insulated, cold-rider skid system over the majority of the furnace length, followed by a single offset of all skids occurring at the transition to a short section of hot-rider skids near the furnace discharge, is sufficient to suppress the final skidmark to a level very close to the minimum achievable with that particular skid design.

larger urban park in Vilnius, Vinguis Parkas. The studied area is located near the Neris River and occupies an area of approximately 162 hectares. Inside the park a total of 95 randomly points were selected to measure soil steady infiltration, between April and September of 2016. At each sampling point, 4 infiltration measurements were carried out using a cylinder infiltrometer with 15 cm higher and a diameter of 7 cm (Cerda, 1996). Each experiment has the duration of 1 hour and the measurements of the infiltrated water were carried out 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 minutes (Cerda, 1996). The steadystate infiltration value of each sampling point corresponds to the average value of the 4 measurements. In each point, the 4 measurements were separated by 5 meters to take in account the spatial variability (Neris et al., 2013). In total 380 infiltration tests were carried out (95x4). Previous to data modelling, data normality was assessed using the shapiro wilk-test and homogeneity of the variances, using Levene test, respectively. The original data was not normally distributed and, only respected the Gaussian distribution and heteroscedasticity after a logarithmic transformation. Data modelling was carried out using transformed data. The accuracy of steady-state soil infiltration spatial distribution was carried out testing several interpolation methods, as Inverse Distance to a Weight (IDW) with the power of 1,2,3,4 and 5, Local Polynomial methods, with the power of 1 and 2 Radial Basis Functions - Spline With Tension (SPT), Completely Regularized Spline (CRS), Multiquadratic (MTQ), Inverse Multiquadratic (IMTQ) and Thin Plate Spline (TPS) - and Geostatistical methods as, Ordinary Kriging (OK), Simple Kriging (SK) and Universal Kriging (UK) (Pereira et al., 2015). Methods performance was assessed calculating the Root Square Mean Error (RMSE) from the errors obtained from cross-validation. The results showed that on average steadystate

With regard to its low viscosity, high stability, clarity, film forming and binding properties, oxidised starch has been widely used in various applications specifically in the food, paper, textile, laundry finishing and binding materials industries. A number of methods have been used to produce oxidised starch through reactions with various oxidizing agents, such as hydrogen peroxide, air oxygen, ozone, bromine, chromic acid, permanganate, nitrogen dioxide and hypochlorite. Unfortunately, most of previous works reported in the literatures were focused on the study of reaction mechanism and physicochemical properties characterization of the oxidised starches produced without investigation of the reaction kinetics of the oxidation process. This work aimed to develop a simple kinetic model for UV catalysed hydrogen peroxide oxidation of starch through implementation of steadystate approximation for the radical reaction rates. The model was then verified using experimental data available in the literature. The model verification revealed that the proposed model shows its good agreement with the experimental data as indicated by an average absolute relative error of only 2.45%. The model also confirmed that carboxyl groups are oxidised further by hydroxyl radical. The carbonyl production rate was found to follow first order reaction with respect to carbonyl concentration. Similarly, carboxyl production rate also followed first order reaction with respect to carbonyl concentration. The apparent reaction rate constant for carbonyl formation and oxidation were 6.24 × 104 s-1 and 1.01 × 104 M-1.s-1, respectively. While apparent reaction rate constant for carboxyl oxidation was 4.86 × 104 M-1.s-1.

This study proposes the use of several problems of unstable steadystate convection with variable fluid density in a porous layer of infinite horizontal extent as two-dimensional (2-D) test cases for density-dependent groundwater flow and solute transport simulators. Unlike existing density-dependent model benchmarks, these problems have well-defined stability criteria that are determined analytically. These analytical stability indicators can be compared with numerical model results to test the ability of a code to accurately simulate buoyancy driven flow and diffusion. The basic analytical solution is for a horizontally infinite fluid-filled porous layer in which fluid density decreases with depth. The proposed test problems include unstable convection in an infinite horizontal box, in a finite horizontal box, and in an infinite inclined box. A dimensionless Rayleigh number incorporating properties of the fluid and the porous media determines the stability of the layer in each case. Testing the ability of numerical codes to match both the critical Rayleigh number at which convection occurs and the wavelength of convection cells is an addition to the benchmark problems currently in use. The proposed test problems are modelled in 2-D using the SUTRA [SUTRA-A model for saturated-unsaturated variable-density ground-water flow with solute or energy transport. US Geological Survey Water-Resources Investigations Report, 02-4231, 2002. 250 p] density-dependent groundwater flow and solute transport code. For the case of an infinite horizontal box, SUTRA results show a distinct change from stable to unstable behaviour around the theoretical critical Rayleigh number of 4??2 and the simulated wavelength of unstable convection agrees with that predicted by the analytical solution. The effects of finite layer aspect ratio and inclination on stability indicators are also tested and numerical results are in excellent agreement with theoretical stability criteria and with

A two-dimensional, steady-statemodel of ground-water flow beneath the Nevada Test Site and vicinity has been developed using inverse techniques. The area is underlain by clastic and carbonate rocks of Precambrian and Paleozoic age and by volcanic rocks and alluvium of Tertiary and Quaternary age that have been juxtaposed by normal and strike-slip faulting. Aquifers are composed of carbonate and volcanic rocks and alluvium. Characteristics of the flow system are determined by distribution of low-conductivity rocks (barriers); by recharge originating in the Spring Mountains, Pahranagat, Timpahute, and Sheep Ranges, and in Pahute Mesa; and by underflow beneath Pahute Mesa from Gold Flat and Kawich Valley. Discharge areas (Ash Meadows, Oasis Valley, Alkali Flat, and Furnace Creek Ranch) are upgradient from barriers. Sensitivities of simulated hydraulic heads and fluxes to variations in model parameters were calculated to guide field studies and to help estimate errors in predictions from transport modeling. Hydraulic heads and fluxes are very sensitive to variations in the greater magnitude recharge/discharge terms. Transmissivity at a location may not be the most important transmissivity for determining flux there. Transmissivities and geometries of large barriers that impede flow from Pahute Mesa have major effects on fluxes elsewhere; as their transmissivities are decreased, flux beneath western Jackass Flats and Yucca Mountains is increased as water is diverted around the barriers. Fortymile Canyon is underlain by highly transmissive rocks that cause potentiometric contours to vee upgradient; increasing their transmissivity increases flow through them, and decreases it beneath Yucca Mountain. (USGS)

The problem of deformation of reinforced metal-composite plates is formulated in rectangular Cartesian coordinates using the second version of Timoshenko theory and taking into account the reduced transverse shear resistance of the plates under steady-state creep conditions. A similar model problem of axisymmetric bending of reinforced plates is considered in polar coordinates.

Soil carbon pool is a significant storage of carbon. Unfortunately, the significance of different drivers of this pool is still unknown. In order to predict future feedbacks of soils to climate change at global level, Earth system model (ESMs) are needed. These ESMs have been tested against soil carbon inventories in order to judge whether models can be used for future prediction. Unfortunately results have been poor, and e.g. Guenet et al. 2013 presents a test where soil carbon stocks by ORCHIDEE models are plotted at plot level against measurements without any correlation. Similarly, Todd-Brown et al. (2013) concludes that most ESMs are not able reproduce measured soil carbon stocks at grid level. Here we estimated litter input from trees and understorey vegetation to soil, based national forest inventory 9 data. Both, biomass estimates for trees and for understorey vegetation were smoothed with ordinary kriging methods and thereafter litter input was modeled by dominant tree species. Also regional litter input from natural mortality and harvesting residues were added to the input. Thereafter we applied Yasso07 (Tuomi et al. 2011) and ROMUL (Chertov et al. 2001) soil models to estimate steady-state carbon stocks for mineral soils of Finland on a 10*10 km2 grid. We run Yasso07 model with annual time step and using parameters based on Scandinavian data (Rantakari et al. 2012) and also with parameters based on global data set (Tuomi et al. 2011). ROMUL model was applied with and without soil water holding capacity information. Results were compared against Biosoil measurements of soil carbon stocks (n=521). We found out that the best match between model estimates and measurements by latitudinal bands (n=43) were by ROMUL model with soil water holding capacity, with RMSE of 9.9 Mg C. Second best match was with Yasso07 with Scandinavian parameters, with RMSE of 15.3 Mg C. Results of this study highlight two things, it is essential to run dynamic soil models with time

Due to the diminishing availability of good quality water for irrigation, it is increasingly important that irrigation and salinity management tools be able to target submaximal crop yields and support the use of marginal quality waters. In this work, we present a steady-state irrigated systems mode...

Due to the diminishing availability of good quality water for irrigation, it is increasingly important that irrigation and salinity management tools be able to target submaximal crop yields and support the use of marginal quality waters. In this work, we present a steady-state irrigated systems mod...

Force depression (FD), the reduction of isometric force following active shortening, is a phenomenon of skeletal muscle that has received significant attention in biomechanical and physiological literature, yet the mechanisms underlying FD remain unknown. Recent experiments identified a slower rate of force redevelopment with increasing amounts of steady-state FD, suggesting that FD may be caused, at least in part, by a decrease in cross-bridge binding rate (Corr and Herzog, 2005; Koppes et al., 2014). Herein, we develop a cross-bridge based model of FD in which the binding rate function, f, decreases with the mechanical work performed during shortening. This modification incorporates a direct relationship between steady-state FD and muscle mechanical work (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008), and is consistent with a proposed mechanism attributing FD to stress-induced inhibition of cross-bridge attachments (Herzog, 1998; Maréchal and Plaghki, 1979). Thus, for an increase in mechanical work, the model should predict a slower force redevelopment (decreased attachment rate) to a more depressed steady-state force (fewer attached cross-bridges), and a reduction in contractile element stiffness (Ford et al., 1981). We hypothesized that since this modification affects the cross-bridge kinetics, a corresponding model would be able to account for both transient and steady-state FD behaviors. Comparisons to prior experiments (Corr and Herzog, 2005; Herzog et al., 2000; Kosterina et al., 2008) show that both steady-state and transient aspects of FD, as well as the relationship of FD with respect to speed and amplitude of shortening, are well captured by this model. Thus, this relatively simple cross-bridge based model of FD lends support to a mechanism involving the inhibition of cross-bridge binding, and indicates that cross-bridge kinetics may play a critical role in FD. PMID:26928777

larger urban park in Vilnius, Vinguis Parkas. The studied area is located near the Neris River and occupies an area of approximately 162 hectares. Inside the park a total of 95 randomly points were selected to measure soil steady infiltration, between April and September of 2016. At each sampling point, 4 infiltration measurements were carried out using a cylinder infiltrometer with 15 cm higher and a diameter of 7 cm (Cerda, 1996). Each experiment has the duration of 1 hour and the measurements of the infiltrated water were carried out 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 minutes (Cerda, 1996). The steadystate infiltration value of each sampling point corresponds to the average value of the 4 measurements. In each point, the 4 measurements were separated by 5 meters to take in account the spatial variability (Neris et al., 2013). In total 380 infiltration tests were carried out (95x4). Previous to data modelling, data normality was assessed using the shapiro wilk-test and homogeneity of the variances, using Levene test, respectively. The original data was not normally distributed and, only respected the Gaussian distribution and heteroscedasticity after a logarithmic transformation. Data modelling was carried out using transformed data. The accuracy of steady-state soil infiltration spatial distribution was carried out testing several interpolation methods, as Inverse Distance to a Weight (IDW) with the power of 1,2,3,4 and 5, Local Polynomial methods, with the power of 1 and 2 Radial Basis Functions - Spline With Tension (SPT), Completely Regularized Spline (CRS), Multiquadratic (MTQ), Inverse Multiquadratic (IMTQ) and Thin Plate Spline (TPS) - and Geostatistical methods as, Ordinary Kriging (OK), Simple Kriging (SK) and Universal Kriging (UK) (Pereira et al., 2015). Methods performance was assessed calculating the Root Square Mean Error (RMSE) from the errors obtained from cross-validation. The results showed that on average steadystate

A three-dimensional, thermo-mechanically coupled model is applied to the Greenland ice sheet. The model implements the full-Stokes equations for the ice dynamics, and the system is solved with the finite-element method (FEM) using the open source multi-physics package Elmer (http://www.csc.fi/elmer/). The finite-element mesh for the computational domain has been created using the Greenland surface and bedrock DEM data with a spatial resolution of 10 km. The study is particularly aimed at better understanding the ice dynamics near the major Greenland ice streams. For this purpose, mesh refinement to obtain improved computed solutions on these areas has been introduced. The meshing procedure starts with the bedrock footprint where a mesh with triangle elements and a resolution of 5 km are employed at the vicinities of the North-East Greenland Ice Stream (NEGIS) and the Jakobshavn (JIS), Kangerdlugssuaq (KL) and Helheim (HH) ice streams. A size function is then applied so that the mesh resolution becomes coarser away of the ice streams up to a maximum horizontal element size of 20 km. The final three-dimensional mesh is obtained by extruding the 2D footprint with 10 vertical layers, so that the resulting mesh contains 118944 prism elements and 69170 nodes. The numerical solution of the Stokes and the heat transfer equations involves direct and iterative solvers depending on the simulation case, and both methods are coupled with stabilization procedures. The boundary conditions are such that the temperature at the surface is parameterized as a function of the latitude and the surface elevation, the geothermal heat flux at the bedrock is prescribed as spatially constant and the lateral sides are open boundaries. The simulations have been conducted in order to obtain steady-state results for the velocity and temperature fields for the entire ice sheet. The model computes the results with both bedrock sliding and melting used alternatively so that their effects on

High-power-density, segmented, thermoelectric (TE) elements have been intimately integrated into heat exchangers, eliminating many of the loss mechanisms of conventional TE assemblies, including the ceramic electrical isolation layer. Numerical models comprising simultaneously solved, nonlinear, energy balance equations have been created to simulate these novel architectures. Both steady-state and transient models have been created in a MATLAB/Simulink environment. The models predict data from experiments in various configurations and applications over a broad range of temperature, flow, and current conditions for power produced, efficiency, and a variety of other important outputs. Using the validated models, devices and systems are optimized using advanced multiparameter optimization techniques. Devices optimized for particular steady-state operating conditions can then be dynamically simulated in a transient operating model. The transient model can simulate a variety of operating conditions including automotive and truck drive cycles.

We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensional flow) in the incompressible limit, which enables us to study the response of suspended macromolecules to the flow by computer simulations. The flow field in this flow is defined by v(x) = εx, where v(x) is the velocity of the fluid and ε is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow in a channel of uniform square cross section with periodic boundary conditions in directions perpendicular to the flow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfect elongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretching rheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry by exponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in our simulations. The fluid particles added along the length of the tube are the same fluid particles which exit the channel due to the flow; thus mass conservation is maintained in our model by default. We also suggest a scheme for possible realization of exponential-stretching flow in experiments. To establish our method as a useful tool to study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volume interactions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers in the fluid to study their responses to the exponential-stretched flow and show that the responses of macromolecules in the two flows are very similar. We demonstrate that the variation of number density of the suspended colloids along the direction of flow is in tune with our expectations. We also conclude from our study of the deformation of star polymers with different numbers of arms f that the critical flow gradient ε

We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensional flow) in the incompressible limit, which enables us to study the response of suspended macromolecules to the flow by computer simulations. The flow field in this flow is defined by vx=ɛx, where vx is the velocity of the fluid and ɛ is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow in a channel of uniform square cross section with periodic boundary conditions in directions perpendicular to the flow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfect elongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretching rheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry by exponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in our simulations. The fluid particles added along the length of the tube are the same fluid particles which exit the channel due to the flow; thus mass conservation is maintained in our model by default. We also suggest a scheme for possible realization of exponential-stretching flow in experiments. To establish our method as a useful tool to study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volume interactions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers in the fluid to study their responses to the exponential-stretched flow and show that the responses of macromolecules in the two flows are very similar. We demonstrate that the variation of number density of the suspended colloids along the direction of flow is in tune with our expectations. We also conclude from our study of the deformation of star polymers with different numbers of arms f that the critical flow gradient ɛc at which

We address the issue of extending thermodynamics to nonequilibrium steadystates. Using driven stochastic lattice gases, we ask whether consistent definitions of an effective chemical potential μ, and an effective temperature Te, are possible. These quantities are determined via zero-flux conditions of particles and energy between the driven system and a reservoir. For the models considered here, the fluxes are given in terms of certain stationary average densities, eliminating the need to perturb the system by actually exchanging particles; μ and Te are thereby obtained via open-circuit measurements, using a virtual reservoir. In the lattice gas with nearest-neighbor exclusion, temperature is not relevant, and we find that the effective chemical potential, a function of density and drive strength, satisfies the zeroth law, and correctly predicts the densities of coexisting systems. In the Katz-Lebowitz-Spohn driven lattice gas, both μ and Te need to be defined. We show analytically that the zeroth law is violated, and determine the size of the violations numerically. Our results highlight a fundamental inconsistency in the extension of thermodynamics to nonequilibrium steadystates. Research supported by CNPq, Brazil.

Wavelet method is a recently developed tool in applied mathematics. The mathematical model of the steady-state immobilized enzyme electrodes is discussed. This theoretical model is based on one-dimensional heat conduction equations containing a non-linear term related to Michaelis-Menten kinetics. An efficient Chebyshev wavelet-based technique is applied to solve the non-linear diffusion equation for the steady-state condition. A simple expression of the substrate concentration is obtained as a function of the Thiele modulus [Formula: see text] and [Formula: see text](kinetic parameter). The wavelet results are compared with the numerical and HPM solutions and found to be in good agreement. PMID:27161606

A three-dimensional, thermo-mechanically coupled model is applied to the Greenland ice sheet. The model implements the full-Stokes equations for the ice dynamics, and the system is solved with the finite-element method (FEM) using the open source multi-physics package Elmer (http://www.csc.fi/elmer/). The finite-element mesh for the computational domain has been created using the Greenland surface and bedrock DEM data with a spatial resolution of 5 km (Bamber and others, 2001). The study is particularly aimed at better understanding the ice dynamics near the major Greenland ice streams. For this purpose, mesh refinement to obtain improved computed solutions on these areas has been introduced. The meshing procedure starts with the bedrock footprint where a mesh with triangle elements and a resolution of 1 km are employed at the vicinities of the North-East Greenland Ice Stream (NEGIS) and the Jakobshavn (JIS), Kangerdlugssuaq (KL) and Helheim (HH) ice streams. A size function is then applied so that the mesh resolution becomes coarser away of the ice streams up to a maximum horizontal element size of 20 km. The final three-dimensional mesh is obtained by extruding the 2D footprint with 10 vertical layers, so that the resulting mesh contains 230760 prism elements and 132740 nodes. The numerical solution of the Stokes and the heat transfer equations involves direct and iterative solvers depending on the simulation case, and both methods are coupled with stabilization procedures. The boundary conditions are such that the temperature at the surface is parameterized as a function of the latitude and the surface elevation, the geothermal heat flux at the bedrock is prescribed as spatially constant and the lateral sides are open boundaries. The simulations have been conducted in order to obtain steady-state results for the velocity and temperature fields for the entire ice sheet. The model computes the results with both bedrock sliding and melting used alternatively so

The correct design and optimization of complex energy systems requires the ability to reproduce the dynamic thermal behavior of each system component. In ground source heat pump (GSHP) systems, modelling the borehole heat exchangers (BHE) dynamic response is especially relevant in the development of control strategies for energy optimization purposes. Over the last years, several models have been developed but most of them are based on steady- state approaches, which makes them unsuitable for short-term simulation purposes. In fact, in order to accurately predict the evolution of the fluid temperatures due to the ON/OFF cycles of the heat pump, it is essential to correctly characterize the dynamic response of BHE for very short time periods. The aim of the present paper is to compare the performance of an analytical steady-statemodel, available in TRNSYS environment (Type 557), with a novel short-term dynamic model. The new dynamic model is based on the thermal-network approach coupled with a vertical discretization of the borehole which takes into account both the advection due to the fluid circulating along the U-tube, and the heat transfer in the borehole and in the ground. These two approaches were compared against experimental data collected from a real GSHP system installed at the Universitat Politecnica de Valencia. The analysis was performed comparing the outlet temperature profiles predicted by both models during daily standard ON/OFF operating conditions, both in heating and cooling mode, and the between both approaches were highlighted. Finally, the obtained results have been discussed focusing on the potential impact that the differences found in the prediction of the temperature evolution could have in design and optimization of GSHP systems.

The results of analyses of the steady-state kinetics of the vacuolar H(+)-translocating pyrophosphatase (V-PPase) of native tonoplast vesicles isolated from etiolated hypocotyls of Vigna radiata (mung bean) and purified enzyme from the same source under a wide range of Mg2+, pyrophosphate (PPi) and K+ concentrations are consistent with a minimal reaction scheme in which dimagnesium pyrophosphate is the active substrate species and catalysis is mediated by preformed enzyme-Mg2+ complex. When account is taken of the sensitivity of the V-PPase to ionic strength, additional kinetic interactions are not required to describe the behavior of the enzyme. N-Ethylmaleimide-protection assays show that the dissociation constant for Mg2+ binding in the absence of PPi is an order of magnitude smaller than that estimated from the steady-state kinetics of PPi hydrolysis. Two distinct Mg(2+)-binding sites are therefore invoked. Since the protective action of Mg2+ is independent of the nature of the monovalent cations and Mg2+ and K+ do not compete during substrate hydrolysis, divalent and monovalent cations are concluded to bind at separate sites. The pH dependencies of the kinetic parameters are consistent with the participation of groups of pKa 5.7 and 8.6 in substrate binding and groups of pKa 6.1 and 9.0 in the substrate-conversion step, indicating that at least four ionizable groups are essential for catalysis. These findings are discussed with respect to the reaction mechanism of the V-PPase and the potential regulatory significance of cytosolic free Mg2+ and K+ in vivo. PMID:8223618

Decomposition is a large term in the global carbon budget, but models of the earth system that simulate carbon cycle-climate feedbacks are largely untested with respect to litter decomposition. Here, we demonstrate a protocol to document model performance with respect to both long-term (10 year) litter decomposition and steady-state soil carbon stocks. First, we test the soil organic matter parameterization of the Community Land Model version 4 (CLM4), the terrestrial component of the Community Earth System Model, with data from the Long-term Intersite Decomposition Experiment Team (LIDET). The LIDET dataset is a 10-year study of litter decomposition at multiple sites across North America and Central America. We show results for 10-year litter decomposition simulations compared with LIDET for 9 litter types and 20 sites in tundra, grassland, and boreal, conifer, deciduous, and tropical forest biomes. We show additional simulations with DAYCENT, a version of the CENTURY model, to ask how well an established ecosystem model matches the observations. The results reveal large discrepancy between the laboratory microcosm studies used to parameterize the CLM4 litter decomposition and the LIDET field study. Simulated carbon loss is more rapid than the observations across all sites, despite using the LIDET-provided climatic decomposition index to constrain temperature and moisture effects on decomposition. Nitrogen immobilization is similarly biased high. Closer agreement with the observations requires much lower decomposition rates, obtained with the assumption that nitrogen severely limits decomposition. DAYCENT better replicates the observations, for both carbon mass remaining and nitrogen, without requirement for nitrogen limitation of decomposition. Second, we compare global observationally-based datasets of soil carbon with simulated steady-state soil carbon stocks for both models. The models simulations were forced with observationally-based estimates of annual

As part of the Southwest Alluvial Basins study, model was constructed to simulate the alluvial aquifer system underlying the Albuquerque-Belen Basin. The model was used to simulate the steady-state flow condition assumed to have existed prior to 1960. Until this time there apparently were no long-term groundwater level changes of a significant magnitude outside the immediate vicinity of Albuquerque. Therefore, the construction of a steady-state flow model of the aquifer system based on reported hydrologic data predating 1960 was justified. During construction of the steady-statemodel, simulated hydraulic conductivity values were adjusted, within acceptable physical limits, until a best fit between measured or reported and computed heads at 34 control wells was achieved. The modeled area was divided into six sub-areas, or zones, within each of which hydraulic conductivity was assumed to be uniform. The model consisted of six layers for each of which simulated transmissivity was proportional to the layer thickness. Adjustments to simulated hydraulic conductivity values in the different zones resulted in final values that ranged from a low of 0.25 ft/day in the west to 50 ft/day in the eastern part of the basin. The error of the simulation, defined as the absolute difference between the computed and the measured or reported water level at the corresponding point in the physical system being modeled, ranged from 0.6 ft to 36 ft, with an average of 14.6 ft for the 34 control wells. (Author 's abstract)

The BEM algorithm developed earlier for steady-state experiments in the scanning electrochemical microscopy (SECM) feedback mode has been expanded to allow for the treatment of more than one independently diffusing species. This allows the treatment of substrate-generation/tip-collection SECM experiments. The simulations revealed the interrelation of sample layout, local kinetics, imaging conditions, and the quality of the obtained SECM images. Resolution in the SECM SG/TC images has been evaluated, and it depends on several factors. For most practical situations, the resolution is limited by the diffusion profiles of the sample. When a dissolved compound is converted at the sample (e.g., oxygen reduction or enzymatic reaction at the sample), the working distance should be significantly larger than in SECM feedback experiments (ca. 3 r(T) for RG = 5) in order to avoid diffusional shielding of the active regions on the sample by the UME body. The resolution ability also depends on the kinetics of the active regions. The best resolution can be expected if all the active regions cause the same flux. In one simulated example, which might mimic a possible scenario of a low-density protein array, considerable compromises in the resolving power, were noted when the flux from two neighboring spots differs by more than a factor of 2. PMID:16898739

A two-dimensional steady-statemodel of the water-table aquifer of the Mullica River basin was made to evaluate the flow system and data required to simulate it. The Mullica River basin covers 570 sq mi and is drained by numerous shallow streams. The water-table aquifer consists of sand and gravel intermixed with clay and silt. The computer model is based on a finite-difference method with stream-seepage equations coupled to the groundwater equation. The model was applied to the approximately steady-state conditions of March 1979. Initial estimates of streambed hydraulic conductance and aquifer hydraulic conductivity were adjusted until model water level matched measured water level within 5 ft for 41 of 42 wells. Also, model streamflow was within 20 percent of measured streamflow at 12 of 15 sites. The 5,000-ft grid spacing should be adequate for a future predictive model. The natural flow system is adequately simulated by a two-dimensional model. (USGS)

Three-dimensional steady-state and transient models of groundwater flow and advective transport in the eastern Snake River Plain aquifer were developed by the U.S. Geological Survey in cooperation with the U.S. Department of Energy. The steady-state and transient flow models cover an area of 1,940 square miles that includes most of the 890 square miles of the Idaho National Laboratory (INL). A 50-year history of waste disposal at the INL has resulted in measurable concentrations of waste contaminants in the eastern Snake River Plain aquifer. Model results can be used in numerical simulations to evaluate the movement of contaminants in the aquifer. Saturated flow in the eastern Snake River Plain aquifer was simulated using the MODFLOW-2000 groundwater flow model. Steady-state flow was simulated to represent conditions in 1980 with average streamflow infiltration from 1966-80 for the Big Lost River, the major variable inflow to the system. The transient flow model simulates groundwater flow between 1980 and 1995, a period that included a 5-year wet cycle (1982-86) followed by an 8-year dry cycle (1987-94). Specified flows into or out of the active model grid define the conditions on all boundaries except the southwest (outflow) boundary, which is simulated with head-dependent flow. In the transient flow model, streamflow infiltration was the major stress, and was variable in time and location. The models were calibrated by adjusting aquifer hydraulic properties to match simulated and observed heads or head differences using the parameter-estimation program incorporated in MODFLOW-2000. Various summary, regression, and inferential statistics, in addition to comparisons of model properties and simulated head to measured properties and head, were used to evaluate the model calibration. Model parameters estimated for the steady-state calibration included hydraulic conductivity for seven of nine hydrogeologic zones and a global value of vertical anisotropy. Parameters

Aiming to improve its knowledge of CFB boilers, EDF has initiated a R and D program including: laboratory work on mock-ups, numerical modelling and on-site tests in CFB power plants. One of the objectives of this program is the development of a comprehensive steady-state1Dmodel of the solid circulation loop, named SILVA, for plant operation and design evaluation purposes. This paper describes its mathematical and physical modelling. Promising validation of the model on cold mock-up and industrial CFB is presented.

In 1987, Grinspoon proposed that the data on hydrogen abundance, isotopic composition, and escape rate were consistent with the hypothesis that water on Venus might be in steadystate rather than monotonic decline since the dawn of time. This conclusion was partially based on a derived water lifetime against nonthermal escape of approximately 10(exp 8) yr. De Bergh et al., preferring the earlier Pioneer Venus value of 200 ppm water to the significantly lower value detected by Bezard et al., found H2O lifetimes of greater than 10(exp 9) yr. Donahue and Hodges derived H2O lifetimes of 0.4-5 x 10 (exp 9) yr. Both these analyses used estimates of H escape flux between 0.4 x 10(exp 7) and 1 x 10(exp 7) cm(exp -2)s(exp -1) from Rodriguez et al. Yet in more recent Monte Carlo modeling, Hodges and Tinsley found an escape flux due to charge exchange with hot H(+) of 2.8 x 10(exp 7) cm(exp -2)s(exp -1). McElroy et al. estimated an escape flux of 8 x 10(exp 6) cm(exp -2)s(exp -1) from collisions with hot O produced by dissociative recombination of O2(+). Brace et al. estimated an escape flux of 5 x 10(exp 6) cm(exp -2)s(exp -1) from ion escape from the ionotail of Venus. The combined estimated escape flux from all these processes is approximately 4 x 10(exp 7) cm(exp -2)s(exp -1). The most sophisticated analysis to date of near-IR radiation from Venus' nightside reveals a water mixing ratio of approximately 30 ppm, suggesting a lifetime against escape for water of less than 10(exp 8) yr. Large uncertainties remain in these quantities, yet the data point toward a steadystate. Further evaluation of these uncertainties, and new evolutionary modeling incorporating estimates of the outgassing rate from post-Magellan estimates of the volcanic resurfacing rate are presented.

Cumulative volcano volume curves are presented as evidence for steady-state behavior at certain volcanoes and to develop a model of steady-state volcanism. A minimum criteria of five eruptions over a year was chosen to characterize a steady-state volcano. The subsequent model features a constant head of magmatic pressure from a reservoir supplied from depth, a sawtooth curve produced by the magma arrivals or discharge from the subvolcanic reservoir, large volume eruptions with long repose periods, and conditions of nonsupply of magma. The behavior of Mts. Etna, Nyamuragira, and Kilauea are described and show continuous levels of plasma output resulting in cumulative volume increases. Further discussion is made of steady-state andesitic and dacitic volcanism, long term patterns of the steadystate, and magma storage, and the lack of a sufficient number of steady-state volcanoes in the world is taken as evidence that further data is required for a comprehensive model.

Presented is a concise and critical account of developments in nonequilibrium thermodynamics. The criterion for stability of nonequilibrium steadystates is critically examined for consecutive and monomolecular triangular reactions, autocatalytic reactions, auto-inhibited reactions, and the Lotka-Volterra model. (JN)

After summarizing the essential elements of a gun-sustained spheromak, the potential for a steady-state is explored by means of a comprehensive physics/engineering/costing model. A range of cost-optimized reactor design point is presented, and the sensitivity of cost to key physics, engineering, and operational variables is reported.

The NASA Lewis Research Center is developing analytical methods and software tools to create a bridge between the controls and computational fluid dynamics (CFD) disciplines. Traditionally, control design engineers have used coarse nonlinear simulations to generate information for the design of new propulsion system controls. However, such traditional methods are not adequate for modeling the propulsion systems of complex, high-speed vehicles like the High Speed Civil Transport. To properly model the relevant flow physics of high-speed propulsion systems, one must use simulations based on CFD methods. Such CFD simulations have become useful tools for engineers that are designing propulsion system components. The analysis techniques and software being developed as part of this effort are an attempt to evolve CFD into a useful tool for control design as well. One major aspect of this research is the generation of linear models from steady-state CFD results. CFD simulations, often used during the design of high-speed inlets, yield high resolution operating point data. Under a NASA grant, the University of Akron has developed analytical techniques and software tools that use these data to generate linear models for control design. The resulting linear models have the same number of states as the original CFD simulation, so they are still very large and computationally cumbersome. Model reduction techniques have been successfully applied to reduce these large linear models by several orders of magnitude without significantly changing the dynamic response. The result is an accurate, easy to use, low-order linear model that takes less time to generate than those generated by traditional means. The development of methods for generating low-order linear models from steady-state CFD is most complete at the one-dimensional level, where software is available to generate models with different kinds of input and output variables. One-dimensional methods have been extended

The ORNL Heat Pump Design Model is a FORTRAN-IV computer program to predict the steady-state performance of conventional, vapor compression, electrically-driven, air-to-air heat pumps in both heating and cooling modes. This model is intended to serve as an analytical design tool for use by heat pump manufacturers, consulting engineers, research institutions, and universities in studies directed toward the improvement of heat pump performance. The Heat Pump Design Model allows the user to specify: system operating conditions, compressor characteristics, refrigerant flow control devices, fin-and-tube heat exchanger parameters, fan and indoor duct characteristics, and any of ten refrigerants. The model will compute: system capacity and COP (or EER), compressor and fan motor power consumptions, coil outlet air dry- and wet-bulb temperatures, air- and refrigerant-side pressure drops, a summary of the refrigerant-side states throughout the cycle, and overall compressor efficiencies and heat exchanger effectiveness. This report provides thorough documentation of how to use and/or modify the model. This is a revision of an earlier report containing miscellaneous corrections and information on availability and distribution of the model--including an interactive version.

Options for faculty utilization in a steadystate are examined, with consideration for their economy or ability to increase turnover or flexibility: early retirement, part retirement, retraining, exchange with other institutions or industry, and fixed-term appointments or lecturer positions. (MSE)

Current models using U- and Th-series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady-state situation. These models have limited applicability to the vadose zone (UZ) where the concentration and migratory behavior of radioisotopes in fluid are often transitory. We present here, as a first attempt of its kind, a model simulating the non-steadystate, intermittent fluid transport in vadose layers. It provides quantitative constraints on in-situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock-water interaction (or water transit) time. For uranium, the simulation predicts that intermittent flushing in the UZ leads to a linear relationship between reciprocal U concentration and {sup 234}U/{sup 238}U ratio in percolating waters, with the intercept and slope bearing information on the rates of dissolution and {alpha}-recoil of U isotopes, respectively. The general validity of the model appears to be borne out by the measurement of uranium isotopes in UZ waters collected at various times over a period during 1995-2006 from a site in the Pena Blanca mining district, Mexico, where the Nopal I uranium deposit is located. Enhanced {sup 234}U/{sup 238}U ratios in vadose-zone waters resulting from lengthened non-flushing time as prescribed by the model provide an interpretative basis for using {sup 234}U/{sup 238}U in cave calcites to reconstruct the regional changes in hydrology and climate. We also provide a theoretical account of the model's potential applications using radium isotopes.

Current models using U- and Th-series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady-state situation. These models have limited applicability to the vadose zone (UZ) where the concentration and migratory behavior of radioisotopes in fluid are often transitory. We present here, as a first attempt of its kind, a model simulating the non-steadystate, intermittent fluid transport in vadose layers. It provides quantitative constraints on in-situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock-water interaction (or water transit) time. For uranium, the simulation predicts that intermittent flushing in the UZ leads to a linear relationship between reciprocal U concentration and 234U/ 238U ratio in percolating waters, with the intercept and slope bearing information on the rates of dissolution and α-recoil of U isotopes, respectively. The general validity of the model appears to be borne out by the measurement of uranium isotopes in UZ waters collected at various times over a period during 1995-2006 from a site in the Peña Blanca mining district, Mexico, where the Nopal I uranium deposit is located. Enhanced 234U/ 238U ratios in vadose-zone waters resulting from lengthened non-flushing time as prescribed by the model provide an interpretative basis for using 234U/ 238U in cave calcites to reconstruct the regional changes in hydrology and climate. We also provide a theoretical account of the model's potential applications using radium isotopes.

A true-to-mechanism model is proposed, which considers steady-state two-phase flow in porous media (SS2 ϕPM) as a composition of two prototype flows, namely ganglion dynamics (GD) and connected-oil pathway flow (CPF). Coupling of the prototype flows is effected with the simple rule that the macroscopic pressure gradient is the same in both. For a given set of values of the flow system parameters, a domain of admissible flow combinations is obtained. The solution is determined by assuming that each point in this domain has equal probability of being `visited'. This leads to unique values for the flow arrangement variables (FAV), the rate of mechanical energy dissipation, and the relative permeabilities. The new model accounts for the non-linearity of the flow as well as for the effects of all the system parameters (notably those affecting interfaces), and its predictions are in very good agreement with existing data.

The scientific payload aboard the stratospheric aircraft M55 Geophysica consists of both in-situ and remote sensing instruments deployed to validate the ENVISAT chemical payload - SCIAMACHY, MIPAS-E and GOMOS during dedicated field campaigns: July and October 2002, Forli (Italy) and February - March 2003, Kiruna (Sweden). Along with the precise measurements required for correct validation procedures, it is necessary to provide additional information related to certain relationships between the available geophysical parameters in order to allow us to better interpret retrieved results, both from the space and from the aircraft measurements. In this regard NO2/NO ratio is inferred/tested along the flight tracks and used to verify the existence of a steadystate photochemical equilibrium, using the data obtained by GASCOD-A/4π, FOZAN and SIOUX instruments. The obtained experimental ratio is compared to that derived from model calculations. A short description of the instruments and flight conditions are described also.

The GOCE satellite mission has significantly contributed to various applications such as solid earth physics, oceanography and geodesy. Some substantial applications of geodesy are to improve the gravity field knowledge and the precise geoid modelling towards realising global height unification. This paper aims to evaluate GOCE geoid model based on the recent GOCE Global Geopotential Model (GGM), as well as EGM2008, using GPS levelling data over East Malaysia, i.e. Sabah and Sarawak. The satellite GGMs selected in this study are the GOCE GGM models which include GOCE04S, TIM_R5 and SPW_R4, and the EGM2008 model. To assess these models, the geoid heights from these GGMs are compared to the local geometric geoid height. The GGM geoid heights was derived using EGMLAB1 software and the geometric geoid height was computed by available GPS levelling information obtained from the Department Survey and Mapping Malaysia. Generally, the GOCE models performed better than EGM2008 over East Malaysia and the best fit GOCE model for this region is the TIM_R5 model. The TIM_R5 GOCE model demonstrated the lowest R.M.S. of ± 16.5 cm over Sarawak, comparatively. For further improvement, this model should be combined with the local gravity data for optimum geoid modelling over East Malaysia.

A hydrocarbon emissions model was developed to study the hydrocarbon emissions mechanisms pertinent to small utility engines. The model considered unburned hydrocarbon emissions from oil film absorption and desorption, and crevice flows. The model was calibrated and validated using experimental data from three typical, small utility engines. These engines were four-stroke, forced-air cooled, carbureted, spark-ignition designs. A specially designed low inertia hydraulic dynamometer was used to test the engines under the SAE J1088 A Cycle at different loads, speeds, and air-fuel ratios. The exhaust emissions of the engines were analyzed using dilute sampling. Reasonably good agreement between model predictions and experimental results was obtained. Subsequently, parametric studies indicated that the model can correctly predict expected hydrocarbon emission trends at different engine operating conditions.

After the simplified version of the 41-Node Stolwijk Metabolic Man Model was implemented on the Sigma 3 and UNIVAC 1110 computers in batch mode, it became desirable to make certain revisions. First, the availability of time-sharing terminals makes it possible to provide the capability and flexibility of conversational interaction between user and model. Secondly, recent physiological studies show the need to revise certain parameter values contained in the model. Thirdly, it was desired to make quantitative and accurate predictions of evaporative water loss for humans in an orbiting space station. The result of the first phase of this effort are reported.

This paper reports the results of numerical studies of axisymmetric flows in a coaxial plasma accelerator in the presence of a longitudinal magnetic field. The calculations were performed using a two-dimensional two-fluid magnetohydrodynamic model taking into account the Hall effect and the conductivity tensor of the medium. The numerical experiments confirmed the main features of the plasmadynamic processes found previously using analytical and one-fluid models and made it possible to study plasma flows near the electrodes.

Human and mouse respiratory tracts show anatomical and physiological differences, which will benefit from alternative experimental models for studying many respiratory diseases. Pig has been recognized as a valuable biomedical model, in particular for lung transplantation or pathologies such as cystic fibrosis and influenza infection. However, there is a lack of knowledge about the porcine respiratory immune system. Here we segregated and studied six populations of pig lung dendritic cells (DCs)/macrophages (Mθs) as follows: conventional DCs (cDC) 1 and cDC2, inflammatory monocyte-derived DCs (moDCs), monocyte-derived Mθs, and interstitial and alveolar Mθs. The three DC subsets present migratory and naive T-cell stimulation capacities. As observed in human and mice, porcine cDC1 and cDC2 were able to induce T-helper (Th)1 and Th2 responses, respectively. Interestingly, porcine moDCs increased in the lung upon influenza infection, as observed in the mouse model. Pig cDC2 shared some characteristics observed in human but not in mice, such as the expression of FCɛRIα and Langerin, and an intra-epithelial localization. This work, by unraveling the extended similarities of the porcine and human lung DC/Mθ networks, highlights the relevance of pig, both as an exploratory model of DC/Mθ functions and as a model for human inflammatory lung pathologies. PMID:26530136

This paper describes a method for dynamic modeling of the interactions of semivolatile organic compounds (SVOCs) with airborne and settled particulate matter in the indoor environment. This method is fully compatible with the other components within the framework. Despite the unc...

In order to gain a deeper knowledge of the interactions in the coupled tire-pavement-system, e.g. for the future design of durable pavement structures, the paper presents recent results of research in the field of theoretical-numerical asphalt pavement modeling at material and structural level, whereby the focus is on a realistic and numerically efficient computation of pavements under rolling tire load by using the finite element method based on an Arbitrary Lagrangian Eulerian (ALE) formulation. Inelastic material descriptions are included into the ALE frame efficiently by a recently developed unsplit history update procedure. New is also the implementation of a viscoelastic cohesive zone model into the ALE pavement formulation to describe the interaction of the single pavement layers. The viscoelastic cohesive zone model is further extended to account for the normal pressure dependent shear behavior of the bonding layer. Another novelty is that thermo-mechanical effects are taken into account by a coupling of the mechanical ALE pavement computation to a transient thermal computation of the pavement cross-section to obtain the varying temperature distributions of the pavement due to climatic impact. Then, each ALE pavement simulation considers the temperature dependent asphalt material model that includes elastic, viscous and plastic behavior at finite strains and the temperature dependent viscoelastic cohesive zone formulation. The temperature dependent material parameters of the asphalt layers and the interfacial layers are fitted to experimental data. Results of coupled tire-pavement computations are presented to demonstrate potential fields of application.

Pharmacokinetic textbooks state that the (apparent) volume of distribution based on drug concentration in plasma (V or Vbeta) is always greater than the volume of distribution (apparent) under steadystate conditions (Vss), but do not provide a general model-independent mathematical proof. Wagner's mathematical comparison between Vbeta and Vss is based on microscopic rate constants of either specific models and is restricted solely to the two-compartment open body model. Nakashima and Benet utilizing a model-dependent approach showed a mathematical relationship between Vbeta and Vss for a multicompartment model, but again by using microscopic model constants. The limitation of these two above mentioned mathematical comparisons is the necessity of knowledge of the model's structure and its microscopic rate constants. The present article describes a new non-compartmental, model-independent, general mathematical proof for Vbeta to be always greater than Vss. This new method does not require any knowledge of microscopical rate constants and is based solely on an exponentially decreasing function, which is the common way to describe drug disposition following i.v. bolus. PMID:14872558

In hadron colliders such as the LHC, the energy deposited in the superconductors by the particles lost from the beams or coming from the collision debris may provoke quenches detrimental to the accelerator operation. In previous papers, a Network Model has been used to study the thermodynamic behavior of magnet coils and to calculate the quench levels in the LHC magnets for expected beam loss profiles. This model was subsequently used for thermal analysis and design optimization of Nb{sub 3}Sn quadrupole magnets, which LARP (US LHC Accelerator Research Program) is developing for possible use in the LHC luminosity upgrade. For these new magnets, the heat transport efficiency from the coil to the helium bath needs to be determined and optimized. In this paper the study of helium cooling channels and the heat evacuation scheme are presented and discussed.

In groundwater dominated lowland catchments the larger part of precipitation on drained agricultural fields recharges the groundwater or reaches surface waters through subsurface drains. However, shallow subsoil structure deterioration due to sealing or compaction, shallow groundwater tables and long and intense precipitation events facilitate ponding of water at the soil surface. During a rainfall event, the ponded area on the field expands and surface runoff reaches the field boundaries when one or more series of ponds form continuous flow paths to the channels and ditches surrounding the field. To understand catchment discharge characteristics it is important to quantify the relative contributions of different flow routes in a catchment. Also, as surface runoff is the main contributor of pesticides and one of the main contributors of phosphorus to surface-water bodies, it plays an important role with regard to the contamination, the eutrophication, and the implications for ecological functioning of aquatic ecosystems. In order to further quantify the relations between groundwater conditions, infiltration rates, and ponding and surface runoff, we developed a computer model that incorporates the saturated, unsaturated zones and a heterogeneous surface topography. The simplifications underlying the model are: The surface microtopography is static, therefore the configuration of ponds and their spill points to other ponds can be determined before the actual model simulation and stored in a database. The unsaturated zone is in hydrostatic equilibrium, therefore there is a unique relationship between the volume of water stored in a soil column and the elevation of the groundwater table. By using the total subsubsurface storage volume as state variable, problems usually associated with saturated-unsaturated zone interactions are bypassed, while still allowing for correct computation of both groundwater flow, and unsaturated zone effects on surface infiltration and thus

The mathematical basis for a computer code PUMA (Plutonium-Uranium-Matrix-Algorithm) is described. The code simulates steady-state concentration profiles of solvent extraction contactors used in the Purex process, directly without first generating the transient behavior. The computational times are reduced, with no loss of accuracy, by about tenfold over those required by codes that generate the steady-state profiles via transient state conditions. Previously developed codes that simulate the steady-state conditions directly are not applicable to partitioning contactors, whereas PUMA is applicable to all contactors in the Purex process. Since most difficulties are encountered with partitioning contactors when simulating steady-state profiles via transient state conditions, it is with these contactors that the greatest saving in computer times is achieved.

We analyzed water temperature, visceral cavity temperature and depth data from archival tags retrieved from bigeye tuna (Thunnus obesus) at liberty in the central Pacific for up to 57 days using a mathematical model of heat exchange. Our model took into account the transfer of heat between the portions of the myotomes comprising red muscle fibers adjacent to the spinal column and served by vascular counter current heat exchanges (henceforth referred to as ;red muscle') and the water, as well as between the red muscle and the temperature sensor of the archival tags in the visceral cavity. Our model successfully predicted the recorded visceral cavity temperatures during vertical excursions provided that the rate constants for heat transfer between the ambient water and the red muscle during cooling (k(low)) and those during heating (k(high)) were very dissimilar. Least-squares fitting of k(low) and k(high) for the entire period that the fish were at liberty yielded values generally in the ranges 0.02-0.04 min(-1) and 0.2-0.6 min(-1) (respectively), with an average ratio k(high)/k(low) of approximately 12. Our results confirmed those from previous studies showing that bigeye tuna have extensive physiological thermoregulatory abilities probably exerted through changes of blood flow patterns that controlled the efficiency of vascular countercurrent heat exchanges. There was a small but significant negative correlation between k(low) and size, whereas there was no correlation between k(high) and size. The maximum swimming speeds during vertical excursions (calculated from the pressure data) occurred midway during ascents and averaged approximately 2 FL s(-1) (where FL=fork length), although speeds as high approximately 4-7 FL s(-1) were also noted. PMID:17644676

In the present study, the interaction of 5-Fluorouracil with herring sperm DNA is reported using spectroscopic and molecular modeling techniques. This binding study of 5-FU with hs-DNA is of paramount importance in understanding chemico-biological interactions for drug design, pharmacy and biochemistry without altering the original structure. The challenge of the study was to find the exact binding mode of the drug 5-Fluorouracil with hs-DNA. From the absorption studies, a hyperchromic effect was observed for the herring sperm DNA in the presence of 5-Fluorouracil and a binding constant of 6.153 × 103 M-1 for 5-Fluorouracil reveals the existence of weak interaction between the 5-Fluorouracil and herring sperm DNA. Ethidium bromide loaded herring sperm DNA showed a quenching in the fluorescence intensity after the addition of 5-Fluorouracil. The binding constants for 5-Fluorouracil stranded DNA and competitive bindings of 5-FU interacting with DNA-EB systems were examined by fluorescence spectra. The Stern-Volmer plots and fluorescence lifetime results confirm the static quenching nature of the drug-DNA complex. The binding constant Kb was 2.5 × 104 L mol-1 and the number of binding sites are 1.17. The 5-FU on DNA system was calculated using double logarithmic plot. From the Forster nonradiative energy transfer study it has been found that the distance of 5-FU from DNA was 4.24 nm. In addition to the spectroscopic results, the molecular modeling studies also revealed the major groove binding as well as the partial intercalation mode of binding between the 5-Fluorouracil and herring sperm DNA. The binding energy and major groove binding as -6.04 kcal mol-1 and -6.31 kcal mol-1 were calculated from the modeling studies. All the testimonies manifested that binding modes between 5-Fluorouracil and DNA were evidenced to be groove binding and in partial intercalative mode.

We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051

The Smith-Lemli-Opitz syndrome (SLOS) is the first-described in a growing family of hereditary defects in cholesterol biosynthesis, and presents with a spectrum of serious abnormalities, including multiple dysmorphologies, failure to thrive, cognitive and behavioral impairments, and retinopathy. Using a pharmacologically induced rat model of SLOS that exhibits key hallmarks of the disease, including progressive retinal degeneration and dysfunction, we show that a high-cholesterol diet can substantially correct abnormalities in retinal sterol composition, with concomitant improvement of visual function, particularly within the cone pathway. Although histologic degeneration still occurred, a high-cholesterol diet reduced the number of pyknotic photoreceptor nuclei, relative to animals on a cholesterol-free diet. These findings demonstrate that cholesterol readily crosses the blood-retina barrier (unlike the blood-brain barrier) and suggest that cholesterol supplementation may be efficacious in treating SLOS-associated retinopathy. PMID:17314682

In this paper we examine the consequences of bubble nucleation mechanism on eruptive degassing of rhyolite magma. We use the results of published high temperature and pressure decompression experiments as input to a modified version of CONFLOW, the numerical model of Mastin and Ghiorso [(2000) U.S.G.S. Open-File Rep. 00-209, 53 pp.] and Mastin [(2002) Geochem. Geophys. Geosyst. 3, 10.1029/2001GC000192] for steady, two-phase flow in vertical conduits. Synthesis of the available experimental data shows that heterogeneous nucleation is triggered at ??P 120-150 MPa, and leads to disequilibrium degassing at extreme H2O supersaturation. In this latter case, nucleation is an ongoing process controlled by changing supersaturation conditions. Exponential bubble size distributions are often produced with number densities of 106-109 bubbles/cm3. Our numerical analysis adopts an end-member approach that specifically compares equilibrium degassing with delayed, disequilibrium degassing characteristic of homogeneously-nucleating systems. The disequilibrium simulations show that delaying nucleation until ??P =150 MPa restricts degassing to within ???1500 m of the surface. Fragmentation occurs at similar porosity in both the disequilibrium and equilibrium modes (???80 vol%), but at the distinct depths of ???500 m and ???2300 m, respectively. The vesiculation delay leads to higher pressures at equivalent depths in the conduit, and the mass flux and exit pressure are each higher by a factor of ???2.0. Residual water contents in the melt reaching the vent are between 0.5 and 1.0 wt%, roughly twice that of the equilibrium model. ?? 2003 Elsevier B.V. All rights reserved.

The steady-state assumption, which states that the production and consumption of metabolites inside the cell are balanced, is one of the key aspects that makes an efficient analysis of genome-scale metabolic networks possible. It can be motivated from two different perspectives. In the time-scales perspective, we use the fact that metabolism is much faster than other cellular processes such as gene expression. Hence, the steady-state assumption is derived as a quasi-steady-state approximation of the metabolism that adapts to the changing cellular conditions. In this article we focus on the second perspective, stating that on the long run no metabolite can accumulate or deplete. In contrast to the first perspective it is not immediately clear how this perspective can be captured mathematically and what assumptions are required to obtain the steady-state condition. By presenting a mathematical framework based on the second perspective we demonstrate that the assumption of steady-state also applies to oscillating and growing systems without requiring quasi-steady-state at any time point. However, we also show that the average concentrations may not be compatible with the average fluxes. In summary, we establish a mathematical foundation for the steady-state assumption for long time periods that justifies its successful use in many applications. Furthermore, this mathematical foundation also pinpoints unintuitive effects in the integration of metabolite concentrations using nonlinear constraints into steady-statemodels for long time periods. PMID:27363728

The hyporheic zone is known to attenuate contaminants originating from surface water, yet the ability of the hyporheic zone to attenuate contaminants in upwelling groundwater plumes as they exit to surface water is less understood. We used MODFLOW and SEAM3D to simulate hyporheic flow cells induced by riverbed dunes and upwelling groundwater together with mixing-dependent denitrification of an upwelling nitrate (NO3-) plume. Our base case modeled labile dissolved organic carbon (DOC) and dissolved oxygen (DO) advecting from surface water, and DO and NO3- advecting from groundwater, typical of certain agricultural areas. We conducted sensitivity analyses that showed mixing-dependent denitrification in the hyporheic zone increased with increasing hydraulic conductivity (K), decreasing lower boundary flux, and increasing DOC in surface water or NO3- in groundwater. Surface water DOC, groundwater NO3-, and K were the most sensitive parameters affecting mixing-dependent denitrification. Nonmixing-dependent denitrification also occurred when there was surface water NO3-, and its magnitude was often greater than mixing-dependent denitrification. Nevertheless, mixing-dependent reactions provide functions that nonmixing-dependent reactions cannot, with potential for hyporheic zones to attenuate upwelling NO3- plumes, depending on geomorphic, hydraulic, and biogeochemical conditions. Stream and river restoration efforts may be able to increase mixing-dependent reactions by promoting natural processes that promote bedform creation and augment labile carbon sources.

The microflow and stirring around paramagnetic particle microchains, referred to as microrotors, are modeled as a circular cylinder rotating about its radial axis at very low Reynolds number. Time scales for momentum transfer under these conditions are determined to be much smaller than those for boundary movement, hence a quasi-steady approximation can be used. The flow is derived at every instant from the case of a steady motion of a horizontally translating cylinder, with the rotation approximated to a series of differential incremental translations. A numerical simulation is used to determine the pathlines and material lines of virtual point fluid elements, which were analyzed to understand the behavior of the flow around the microrotor. The results indicate the flow to be unsteady, with chaotic advection observed in the system. The fluid motion is primarily two-dimensional, parallel to the rotational plane, with mixing limited to the immediate area around the rotating cylinder. Fluid layers, up to many cylinder diameters, in the axial direction experience the disturbance. Elliptic and star shaped pathlines, including periodic orbits, are observed depending on the fluid element's initial location. The trajectories and phase angles compare well with the experimental results, as well as with data from particle dynamics simulations. Material lines and streaklines display stretching and folding, which are indicative of the chaotic behavior and stirring characteristics of the system. The material lines have similar lengths for the same amount of rotation at different speeds, and the effect of rotational speeds appears to be primarily to change the time of mixing. The results are expected to help in the design of a particle microrotor based sensing technique. PMID:15159779

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7 x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the one-dimensional Poisson equation for IEC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with nonfusing hydrogen- 1. The deuterium rates are consistent with predictions from the model.

A computer program based on the Galerkin finite-element method was developed to simulate two-dimensional steady-state ground-water flow in either isotropic or anisotropic confined aquifers. The program may also be used for unconfined aquifers of constant saturated thickness. Constant head, constant flux, and head-dependent flux boundary conditions can be specified in order to approximate a variety of natural conditions, such as a river or lake boundary, and pumping well. The computer program was developed for the preliminary simulation of ground-water flow in the Edwards-Trinity Regional aquifer system as part of the Regional Aquifer-Systems Analysis Program. Results of the program compare well to analytical solutions and simulations .from published finite-difference models. A concise discussion of the Galerkin method is presented along with a description of the program. Provided in the Supplemental Data section are a listing of the computer program, definitions of selected program variables, and several examples of data input and output used in verifying the accuracy of the program.

A one-dimensional model for water flow and solute transport in the unsaturated zone under steady-state or transient flow conditions was developed from the principles of the mixing-cell model. The unsaturated zone is discretized into a series of independent mixing cells. Each cell may have unique hydrologic, lithologic, and sorptive properties. Ordinary differential equations (ODE) describe the material (water and solute) balance within each cell. Water flow equations are derived from the continuity equation assuming that unit-gradient conditions exist at all times in each cell. Pressure gradients are considered implicitly through model discretization. Unsaturated hydraulic conductivity and moisture contents are determined by the material-specific moisture characteristic curves. Solute transport processes included explicit treatment of advective processes, first-order chain decay, and linear sorption reactions. Dispersion is addressed through implicit and explicit dispersion. Implicit dispersion is an inherent feature of all mixing cell models and originates from the formulation of the problem in terms of mass balance around fully mixed volume elements. Expressions are provided that relate implicit dispersion to the physical dispersion of the system. The system of ODEs was solved using a forth-order Runge-Kutta algorithm coupled with adaptive step size control. Computer run times for transient flow and solute transport were typically several seconds on a 2-GHz Intel Pentium IV® desktop computer. The model was benchmarked against analytical solutions and finite-element approximations to the partial differential equations (PDE) describing unsaturated flow and transport. Differences between the maximum solute flux estimated by the mixing-cell model and the PDE models were typically less than 2%.

A theoretical model for the rate of oxidation of pentachlorophenol (PCP) catalyzed by horseradish peroxidase (HRP), was investigated to account for the influence of hydrogen peroxide (H2O2) concentration on the catalytic activity. To evaluate the maximum allowable H2O2 concentration, a relatively simple steady-statemodel was developed based on the Ping-Pong Bi-Bi mechanism considering the effect of excess H2O2. Several sets of experimental data obtained from batch reactions using an equimolar concentration of H2O2 and PCP were used to estimate the kinetic parameters by a nonlinear regression method. The model profiles acquired using the estimated parameters were in good agreement with experimental data at different initial enzyme and substrate concentrations. The best-fitted parameters were used to predict the initial rate of the enzyme reaction. The model prediction was coincident with the experimental results of other studies, indicating that the proposed model could be used for the optimization of reaction conditions. The maximum allowable H2O2 concentration to prevent H2O2 inhibition was calculated from the proposed model equation: [H2O2](0,max) = (square root)KmH2O2Ki[PCP]0/KmPCP+[PCP]0. Using this equation, a curve depicting the non-inactivation zone for the two substrates (hydrogen peroxide and PCP) was plotted and it could be used for experimental design and optimal process operation. To minimize enzyme inactivation by H2O2, it was determined that the concentration of H2O2 should be lower than 2.78 mM, regardless of the stoichiometric ratio. PMID:16232630

The higher charge states found in slow (<400 km s-1) solar wind streams compared to fast streams have supported the hypothesis that the slow wind originates in closed coronal loops and is released intermittently through reconnection. Here we examine whether a highly ionized slow wind can also form along steady and open magnetic field lines. We model the steady-state solar atmosphere using the Alfvén Wave Solar Model (AWSoM), a global MHD model driven by Alfvén waves, and apply an ionization code to calculate the charge state evolution along modeled open field lines. This constitutes the first charge state calculation covering all latitudes in a realistic magnetic field. The ratios {{O}+7}/{{O}+6} and {{C}+6}/{{C}+5} are compared to in situ Ulysses observations and are found to be higher in the slow wind, as observed; however, they are underpredicted in both wind types. The modeled ion fractions of S, Si, and Fe are used to calculate line-of-sight intensities, which are compared to Extreme-ultraviolet Imaging Spectrometer (EIS) observations above a coronal hole. The agreement is partial and suggests that all ionization rates are underpredicted. Assuming the presence of suprathermal electrons improved the agreement with both EIS and Ulysses observations; importantly, the trend of higher ionization in the slow wind was maintained. The results suggest that there can be a sub-class of slow wind that is steady and highly ionized. Further analysis shows that it originates from coronal hole boundaries (CHBs), where the modeled electron density and temperature are higher than inside the hole, leading to faster ionization. This property of CHBs is global and observationally supported by EUV tomography.

It is shown that a Liapunov criterion exists for the stability of nonequilibrium steadystates. This criterion is based upon the fluctuation-dissipation relation, as was first pointed out by Keizer. At steadystates, the Liapunov function is constructed from the covariance matrix for the thermodynamic variables. Unlike the situation around equilibrium, at steadystates the covariance matrix and the “excess entropy” matrix are not equivalent. The excess entropy, which serves as the Liapunov function around equilibrium, does not work in this capacity at steadystates. Keizer's Liapunov function must be viewed as the first correct candidate for a proper Liapunov function for steadystates. PMID:16592649

The Briggs-Haldane assumption is used as the basis for the development of a kinetic model for enzyme catalysis. An alternative definition of the steadystate and examples of realistic mechanisms are provided. (KR)

We previously used data from IODP Expedition 320 and ODP Leg 199 sites to refine the dynamics of the carbonate compensation depth (CCD) in the equatorial Pacific during the Eocene and the Greenhouse-to-Icehouse transition, and were able to determine that the CCD fluctuated about 500m in depth, and that carbonate accumulation rates varied between near zero and ~1.5 g/cm2/kyr. "Carbonate accumulation events" lasted for a time period of around 1 Myr, with sharp transitions into and out of these cycles of enhanced carbonate accumulation. We now present new results investigating CCD behavior in an Earth System Model (GENIE) in steady-state conditions in response to variations in atmospheric CO2, coupled in turn to changes in the net deep-sea weathering supply of alkalinity, to variations in labile vs. refractory organic carbon supply to the sea-floor, to the rain-ratio hypothesis, and to changes in the Mg and Ca seawater composition. We also use a simpler box model (LOSCAR) to evaluate the non-steady-state behavior of the CCD in response to changes in shelf-basin partitioning, and simple changes in ocean circulation patterns. Our modelling reveals that increasing atmospheric CO2 with fixed weathering results in a shallower CCD. This is a consequence of non-linearities in the carbonate system and reflects a deepening of the lysocline at the expense of the CCD and contraction of the lysocline transition zone. When this is combined with the response of increased weathering by activating the full silicate weathering feedback, we find an unexpected result: when progressively increasing the rate of prescribed CO2 outgassing in a series of GENIE experiments, atmospheric CO2 and weathering flux happen to co-vary in such a way that they result in a largely invariant CCD depth. We also investigate the viability of a 'sediment labile organic matter' hypothesis to help explain the CCD fluctuations. We repeat the GENIE net-weathering supply analysis but now change the partitioning

Dear Editor: We are disappointed that Dr. Bogen felt our paper(1) “adds little new” to previously published work utilizing steadystate solutions to PBPK models. Moreover, it was not our intention to be either “dismissive” or “misleading” in our admittedly brief citation of the...

Changes in the West Antarctic Ice Sheet since the end of the last ice age have implications for how we interpret its present behavior, in terms of both its stability and its record of climate history. Siple Dome, the ridge between Ice Streams C and D, is not presently thinning and is close to being in balance with present environmental conditions. We present three independent measurements of ice thickness change in the divide region of Siple Dome: a GPS surface horizontal strain network, fiber optic vertical strain measurements at depth, and precision GPS measurements of vertical motion of near-surface ice ("coffee-can" method). From the horizontal strain network, we calculate the divergence of the horizontal velocity. This divergence is equal to the gradient of vertical velocity at the surface and, with some assumptions about the distribution of strain rates with depth, we can calculate the vertical velocity at the surface. For steadystate, the vertical velocity must be balanced by the local accumulation rate. The fiber optic instruments provide a profile of the relative vertical velocity with depth. We fit a theoretical vertical velocity pattern to these data and extrapolate to find the surface vertical velocity. Our third method (coffee-can) directly measures the vertical motion of a marker 20 meters deep using precision GPS and compares it with the local long-term rate of snow accumulation to calculate the net rate of ice sheet thickness change. All three methods reach the same conclusion: Siple Dome is currently very close to being in steadystate. This result has two implications. First, ice dynamics models developed to interpret radar images or ice core data can assume steadystate behavior, simplifying the models. Second, our result suggests that the central part of the Ross Embayment may have had a low-elevation profile during the late Holocene, even though other areas of the WAIS may have been thicker.

A steady-statemodel of the planktonic food web of the Bizerte Lagoon (Tunisia, South-western Mediterranean) was developed to characterize its structure and functioning through four stations: MA under urban discharge, MB impacted by industrial input, MJ located at proximity of shellfish farming and R in the central area of the lagoon. Carbon stocks of eight chosen compartments were determined and flows were assigned for each one from field data. Missing flow values were calculated by inverse analysis for each station. Network analysis was applied to the resulting food web models to characterize their properties. These analyses mainly showed similarity among stations concerning (1) a high primary production of phytoplankton which was dominated by >10 μm cells (i.e. diatoms); (2) important herbivory against detritivory in stations MA and MJ; (3) major role of detritivory in stations MB and R; (4) efficiency of microbial link in transferring carbon for higher trophic level; (5) efficiency of microzooplankton as a trophic link between detritus, dissolved organic carbon, autotrophs and mesozooplankton; (6) important recycling of carbon leading to conclude about an immature state of the ecosystem. Differences between the functioning of microbial food webs in the lagoon are mainly due to the location of stations. The proximity of station MB to inland and industrial discharges affected its productivity and made it the least productive station. Water circulation into the lagoon made pollutant concentrate into the south and the western sections which seemed to affect the planktonic food web, since the values of productivity reported for stations MB and R were lower than those calculated for the others stations.

We explore simple lattice-gas reaction models for CO-oxidation on 1D and 2D periodic arrays of surface adsorption sites. The models are motivated by studies of CO-oxidation on RuO2(110) at high-pressures. Although adspecies interactions are neglected, the effective absence of adspecies diffusion results in kinetically-induced spatial correlations. A transition occurs from a random mainly CO-populated steady-state at high CO-partial pressure pCO, to a strongly-correlated near-O-covered steady-state for low pCO as noted. In addition, we identify a second transition to a random near-O-covered steady-state at very low pCO.

We explore simple lattice-gas reaction models for CO-oxidation on 1D and 2D periodic arrays of surface adsorption sites. The models are motivated by studies of CO-oxidation on RuO2(110) at high-pressures. Although adspecies interactions are neglected, the effective absence of adspecies diffusion results in kinetically-induced spatial correlations. A transition occurs from a random mainly CO-populated steady-state at high CO-partial pressure pCO, to a strongly-correlated near-O-covered steady-state for low pCO as noted. In addition, we identify a second transition to a random near-O-covered steady-state at very low pCO.

The last twenty years has seen the steady increase in the quality and quantity of streaming potential coefficient and zeta potential determinations in the laboratory. More recently (Glover et al., 2012), a model has been developed that allows both the zeta potential and streaming potential coefficient of a porous rock to be calculated theoretically. We have carried out high quality streaming potential coupling coefficient measurements using a newly designed cell with both a steady-state methodology and a new pressure transient approach. We have shown the pressure transient approach to be particularly good in providing high quality streaming potential coefficient measurements as it allows thousands of measurements to be made at different pressures to which a good linear regression can be fitted. Nevertheless, the method is approximately five times as fast as the conventional measurement approaches. Measurements of streaming potential coefficient have been carried out on seven samples of Berea, Boise and Lochaline sandstones as a function of salinity (approximately 18 salinities between 10-5 M and 2 M) and pH (approximately 11 pHs between 8 and 2). The data have been inverted to obtain the zeta potential. The streaming potential coefficient becomes greater (more negative) for fluids with lower salinities and higher pHs, which is consistent with the corpus of existing measurements. Our measurements are also consistent with the high salinity streaming potential coefficient measurements made by Vinogradov et al. (2010). The streaming potential and zeta potential tend to zero as the pH approaches the point of zero net surface charge for quartz (approximately 3), which was 2.8±0.2 in our measurements. Both the streaming potential coefficient and the zeta potential have also been modelled using the theoretical approach of Glover et al. (2012). This modelling allows the microstructural, electro-chemical and fluid properties of the saturated rock to be taken into account in

The rupture of dry frictional interfaces occurs through the propagation of fronts breaking the contacts at the interface. Recent experiments have shown that the velocities of these rupture fronts range from quasistatic velocities proportional to the external loading rate to velocities larger than the shear wave speed. The way system parameters influence front speed is still poorly understood. Here we study steady-state rupture propagation in a one-dimensional (1D) spring-block model of an extended frictional interface for various friction laws. With the classical Amontons-Coulomb friction law, we derive a closed-form expression for the steady-state rupture velocity as a function of the interfacial shear stress just prior to rupture. We then consider an additional shear stiffness of the interface and show that the softer the interface, the slower the rupture fronts. We provide an approximate closed form expression for this effect. We finally show that adding a bulk viscosity on the relative motion of blocks accelerates steady-state rupture fronts and we give an approximate expression for this effect. We demonstrate that the 1D results are qualitatively valid in 2D. Our results provide insights into the qualitative role of various key parameters of a frictional interface on its rupture dynamics. They will be useful to better understand the many systems in which spring-block models have proved adequate, from friction to granular matter and earthquake dynamics.

The aim of this work concerns the development and the validation of a thermal steadystatemodel applied to a permanent magnet direct current motor with commutator. The rated power of the machine is 120 W. Design has been realized thanks to the thermal modulus of the computation software with the finite element method Flux3D. It is shown in this work how it is possible to use only the heat equation to simulate the thermal behaviour of the motor. It implies calculating of new fluid conductivities (considering also all thermal modes) by comparison of calculated and experimental temperatures. To realize these 3D modelizations, it is necessary to know and to locate all the losses of the motor which are considered as thermal sources. The experimental temperatures are given by 40 chromel-alumel thermocouples of 100 μm diameter located in the rotor and the stator of the machine. Numerical computations use Dirichlet boundary layer conditions given by an IR camera. Ce travail concerne le développement et la validation d'un modèle de simulation du comportement thermique tridimensionnel en régime permanent d'un moteur électrique de 120 watt à courant continu, à aimants permanents et à collecteur. Le logiciel est développé à partir du code de calculs par éléments finis Flux3D. L'équation de la chaleur modélise l'ensemble des transferts thermiques du moteur. Cela nécessite de recaler certains paramètres fluides par comparaison des températures simulées et expérimentales. Une séparation détaillée des différentes pertes est nécessaire pour obtenir une bonne précision finale. Un banc d'essais thermiques permet d'obtenir à l'aide de 40 thermocouples (chromel-alumel de 100 μm de diamètre) les températures au stator et au rotor. Une caméra thermographique infrarouge donne les conditions aux limites de Dirichlet nécessaires à la modélisation.

Preliminary 1D seismic velocity model derived from ambient noise correlation. 28 Green's functions filtered between 4-10 Hz for Vp, Vs, and Qs were calculated. 1Dmodel estimated for each path. The final model is a median of the individual models. Resolution is best for the top 1 km. Poorly constrained with increasing depth.

Steady-state analyses of generic PBPK models for volatile organic chemical (VOC) exposure and risk assessment have been undertaken and applied for nearly two decades now. Chiu and White's paper on this subject adds little new to this earlier work. Their dismissive claim that ''Similar analyses have been done for specific chemicals and for inhalation'' is misleading, because some of this earlier work did indeed focus on ''generic'' PBPK models generally applicable to VOC exposure by multiple routes. In particular, the earliest of these previous studies developed steady-state solutions for generic PBPK models including respiratory and 1-compartment oral routes of exposure, and further specified how to add injection and dermal exposure routes. Chiu and White included a 2-compartment oral pathway and a lung compartment in an otherwise identical generic PBPK model, but did not consider other exposure pathways such as dermal uptake. Each of the earlier studies first presented a steady-state solution to a generic, multiroute PBPK model, and only then applied the generic solution to a problem or illustration involving a specific compound--i.e., the same approach used later by Chiu and White. For example, the earlier study included a simple, intuitive expression for low-dose metabolized fraction f*{sub m} of any applied multiroute dose, allowing route-to-route extrapolation regardless of compound in low-dose contexts that typically are of interest in environmental VOC risk assessment. Section 2.2 of Chiu and White's paper (''Generalization to Time-Varying Exposures'') concludes that, under conditions of virtually linear metabolism, PBPK system ''solutions to steady-state exposures are directly applicable to intermittent exposures''--i.e., under such conditions, all steady-state system solutions (or output states) become valid when each dynamic input is replaced by its corresponding time-weighted average value. This conclusion, a well known axiom of linear systems theory

Steadystate tokamak equilibria without current drive are found. This is made possible by including the potato bootstrap current close to the magnetic axis. Tokamaks with this class of equilibria do not need seed current or current drive, and are intrinsically steadystate. {copyright} {ital 1997} {ital The American Physical Society}

Coupling between continuous-flow, stirred tank reactors (CSTR's), each having multiple steadystates, can produce new steadystates with different concentrations of the chemical species in each of the coupled tanks. In this work, we identify a kinetic potential ψ that governs the deterministic time evolution of coupled tank reactors, when the reaction mechanism permits a single-variable description of the states of the individual tanks; examples include the iodate-arsenous acid reaction, a cubic model suggested by Noyes, and two quintic models. Stable steadystates correspond to minima of ψ, and unstable steadystates to maxima or saddle points; marginally stable states typically correspond to saddle-node points. We illustrate the variation in ψ due to changes in the rate constant for external material intake (k0) and for exchange between tanks (kx). For fixed k0 values, we analyze the changes in numbers and types of steadystates as kx increases from zero. We show that steadystates disappear by pairwise coalescence; we also show that new steadystates may appear with increasing kx, when the reaction mechanism is sufficiently complex. For fixed initial conditions, the steadystate ultimately reached in a mixing experiment may depend on the exchange rate constant as a function of time, kx(t) : Adiabatic mixing is obtained in the limit of slow changes in kx(t) and instantaneous mixing in the limit as kx(t)→∞ while t remains small. Analyses based on the potential ψ predict the outcome of mixing experiments for arbitrary kx(t). We show by explicit counterexamples that a prior theory developed by Noyes does not correctly predict the instability points or the transitions between steadystates of coupled tanks, to be expected in mixing experiments. We further show that the outcome of such experiments is not connected to the relative stability of steadystates in individual tank reactors. We find that coupling may effectively stabilize the tanks. We provide

the next FP reservoir with a lower inundation frequency (we modify the Malmon (2002) model to account for these fluxes). Deposition rates are the product of area and accumulation rates. Erosion rates are then determined that conserve the mass in each reservoir through time. The existing area and elevation range for each FP reservoir is assumed to remain in morphological steadystate, which requires that the area eroded from a particular reservoir is replaced by an equal area transferring in, due to deposition, from a lower elevation reservoir. These functions are constrained by measurements of FP area and mass, the total exchange rate for the FP from the sediment budget, and conservation of mass within each FP sub-reservoir. Our revised model successfully fits Hg concentration histories in the FGCM, reproduces contemporary loading of mercury from bank erosion, and provides reasonable estimates of Hg concentration in the water column. Thus, alluvial sediment storage reservoirs should not be assumed to be well-mixed, and sediment budgets cannot be used to route contaminants through river valleys without accounting for the long-tailed distribution of residence times that may occur in these environments.

A wind-tunnel investigation has been made at low speed to determine the effects of vertical fins placed ahead of the vertical tail on the directional stability and damping-in-yaw characteristics of a swept-wing model under steady-state oscillatory conditions. Various sizes of fins were used above and below the fuselage center line. The vertical-tail size also was varied.

The hydraulic characterization of soil hydraulic properties is a prerequisite to the modelling of flow in the vadose zone. Since many years, numerous methods were developed to determine soil hydraulic properties. Many of these methods rely on water infiltration experiments and their analysis using analytical or numerical models. At the beginning, most models were developed for water infiltration at steadystate. These models had the advantage to be easy to develop from a theoretical point of view. Yet, many drawbacks remain including the need to wait for a long time, leading to time-consuming experiments, the risk to infiltrate water in large volumes of soil, leading to a response affected by soil variability, and the uncertainty regarding the attainment of steadystate (i.e. constant infiltration rate). More recently, infiltration models and mathematical developments addressed the case of consecutive transient and steadystates. Yet, one main problem remain. In the field, the operator is never sure about the state of water infiltration data. This paper present analytical formulations for the estimation of a transition time. We consider the model developed by Haverkamp et al. (1994) linking 1D infiltration flux to cumulative infiltration and related approximated expansions. An analytical method based on scaling is proposed to define transition time values in terms of both scaled cumulative infiltration and times. Dimensional times are then calculated for a large variety of soils and initial conditions. These time database can be considered as a relevant tool for the guidance for operators who conduct water infiltration experiments and wants to know when to stop and also for modelers who want to know how to select the data to fit transient or steadystatemodels. Haverkamp, R., Ross, P. J., Smetten, K. R. J., Parlange, J. Y. (1994), Three-dimensional analysis of infiltration from the disc infiltrometer: 2 Physically based infiltration equation. Water Resour. Res

Continuous processes often exhibit a high proportion of steadystate, and have been modeled with steady-state formulations for thirty years, resulting in very CPU-time efficient computations. On the other hand, incremental forming processes generally remain a challenge for FEM software, because of the local nature of deformation compared with the size of the part to be formed, and of the large number of deformation steps needed. Among them however, certain semi-continuous metal forming processes can be characterized as periodic, or cyclic. In this case, an efficient computational strategy can be derived from the ideas behind the steady-statemodels. This will be illustrated with the example of pilgering, a seamless tube cold rolling process.

The study of alternative steadystates for nitrogen oxides is discussed: The production of these oxides and the reactions they undergo in the atmosphere are described. The computerized modelling of the atmosphere using a one dimensional time dependent photochemical model is attempted.

Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.

This paper presents a GIS-based 1-d distributed overland flow model and summarizes an application to simulate a flood event. The model estimates infiltration using the Green-Ampt approach and routes excess rainfall using the 1-d diffusive wave approximation. The model was designed to use readily available topographic, soils, and land use/land cover data and rainfall predictions from a meteorological model. An assessment of model performance was performed for a small catchment and a large watershed, both in urban environments. Simulated runoff hydrographs were compared to observations for a selected set of validation events. Results confirmed the model provides reasonable predictions in a short period of time.

The morphology of an alluvial river channel affects the movement of water and sediment along it, but in the longer run is shaped by those processes. This interplay has mostly been investigated empirically within the paradigm of Newtonian mechanics. In rivers, this has created an emphasis on equilibrium configurations with simple morphology and uniform steady flow. But transient adjustment, whether between equilibrium states or indefinitely, is to be expected in a world in which hydrology, sediment supply, and base level are not fixed. More fundamentally, water flows and all the phenomena that accompany them are inherently unsteady, and flows in natural channels are characteristically nonuniform. The morphodynamics of alluvial river channels is the striking consequence. In this paper, we develop the essential connection between the episodic nature of bed material transport and the production of river morphology, emphasizing the fundamental problems of sediment transport, the role of bar evolution in determining channel form, the role of riparian vegetation, and the wide range of time scales for change. As the key integrative exercise, we emphasize the importance of physics-based modeling of morphodynamics. We note consequences that can be of benefit to society if properly understood. These include the possibility to better be able to model how varying flows drive morphodynamic change, to understand the influence of the sediments themselves on morphodynamics, and to recognize the inherent necessity for rivers that transport bed material to deform laterally. We acknowledge pioneering contributions in WRR and elsewhere that have introduced some of these themes.

The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of the 2-dimensional bifurcated mixed compression supersonic inlet is being developed. The model utilizes computational fluid dynamics for both the supersonic and subsonic diffusers. The oblique shocks are modeled utilizing compressible flow equations. This model also implements variable geometry required to control the normal shock position. The model is flexible and can also be utilized to simulate other mixed compression supersonic inlet designs. The model was validated both in time and in the frequency domain against the legacy LArge Perturbation INlet code, which has been previously verified using test data. This legacy code written in FORTRAN is quite extensive and complex in terms of the amount of software and number of subroutines. Further, the legacy code is not suitable for closed loop feedback controls design, and the simulation environment is not amenable to systems integration. Therefore, a solution is to develop an innovative, more simplified, mixed compression inlet model with the same steadystate and dynamic performance as the legacy code that also can be used for controls design. The new nonlinear dynamic model is implemented in MATLAB Simulink. This environment allows easier development of linear models for controls design for shock positioning. The new model is also well suited for integration with a propulsion system model to study inlet/propulsion system performance, and integration with an aero-servo-elastic system model to study integrated vehicle ride quality, vehicle stability, and efficiency.

This report describes a quasi-three-dimensional finite-difference model for simulation of steady-state ground-water flow in the Floridan aquifer over a 932-square-mile area that contains 10 municipal well fields. The over-lying surficial aquifer contains a water table and is coupled to the Floridan aquifer by leakage term that represents flow through a confining layer separating the two aquifers. Under the steady-state condition, all storage terms are set to zero. Use of the head-controlled flux condition allows simulated head and flow changes to occur in the Floridan aquifer at the model boundaries. Procedures used to calibrate the model, test its sensitivity to input-parameter errors, and validate its accuracy for predictive purposes are described. Also included are attachments that describe setting up and running the model. Example model-interrogation runs show anticipated drawdowns under high, average, and low recharge conditions with 10 well fields pumping simultaneously at the maximum annual permitted rates totaling 186.9 million gallons per day. (USGS)

A two-dimensional finite-difference model was developed for simulation of steady-state ground-water flow in the Floridan aquifer throughout a 932-square-mile area, which contains nine municipal well fields. The overlying surficial aquifer contains a constant-head water table and is coupled to the Floridan aquifer by a leakage term that represents flow through a confining layer separating the two aquifers. Under the steady-state condition, all storage terms are set to zero. Utilization of the head-controlled flux condition allows head and flow to vary at the model-grid boundaries. Procedures are described to calibrate the model, test its sensitivity to input-parameter errors, and verify its accuracy for predictive purposes. Also included are attachments that describe setting up and running the model. An example model-interrogation run shows anticipated drawdowns that should result from pumping at the newly constructed Cross Bar Ranch and Morris Bridge well fields. (USGS)

A numerical approach for analyzing the forced vibration problem of a symmetrically laminated FRP (fiber reinforced plastic) composite plate was proposed by the authors. In the present paper, this approach is modified for application to an unsymmetrically laminated FRP composite plate. Numerical calculations are carried out for the clamped antisymmetrically laminated rectangular and elliptical plates which are a kind of unsymmetrically laminated plate. Then,, the effects of the lamina material and the fiber orientation angle on the steadystate response are discussed. Furthermore, it is investigated that what structural damping factor is most influenced on the steadystate response of an antisymmetrically laminated plate.

The inductively formed spheromak configuration (S-1) can be maintained in a highly stable and controlled fashion. The method described eliminates the restriction to pulsed spheromak plasmas or the use of electrodes for steady-state operation, and, therefore, is a reactor-relevant formation and sustainment method.

A steadystate society has limits pertaining to population size, non-renewable resources, and production which emits heat or substances into soil, water, or the atmosphere. Respecting these limits means renouncing exponential quantitative growth and accepting a universally available consumption standard. (SW)

The Cantera Opus SteadyState (ca-opusst) applications solves steady reacting flow problems in opposed-flow geometries. It is a 1-0 application that represents axisymmetnc 3-0 physical systems that can be reduced via a similarity transformation to a 1-0 mathematical representation. The code contain solutions of the general dynamic equations for the particle distribution functions using a sectional model to describe the particle distribution function. Operators for particle nucleation, coagulation, condensation (i.e., growth/etching via reactions with themore » gas ambient), internal particle reactions. particle transport due to convection and due to molecular transport, are included in the particle general dynamics equation. Heat transport due to radiation exchange of the environment with particles in local thermal equilibrium to the surrounding gas will be included in the enthalpy conservation equation that is solved for the coupled gas! particle system in an upcoming version of the code due in June 2005. The codes use Cantera , a C++ Cal Tech code, for determination of gas phase species transport, reaction, and thermodynamics physical properties and source terms. The Codes use the Cantera Aerosol Dynamics Simulator (CADS) package, a general library for aerosol modeling, to calculate properties and source terms for the aerosol general dynamics equation, including particle formation from gas phase reactions, particle surface chemistry (growth and oxidation), bulk particle chemistry, particle transport by Brownian diffusion, thermophoresis, and diffusiophoresis, and thermal radiative transport involving particles. Also included are post-processing programs, cajost and cajrof, to extract ascii data from binary output files to produce plots.« less

A sub Kelvin Active Magnetic Regenerative Refrigerator (AMRR) is being developed at the University of Wisconsin - Madison. This AMRR consists of two circulators, two regenerators, one superleak, one cold heat exchanger, and two warm heat exchangers. The circulators are novel non-moving part pumps that reciprocate a superfluid mixture of 4He-3He in the system. Heat from the mixture is removed within the two regenerators of this tandem system. An accurate model of the regenerators in this AMRR is necessary in order to predict the performance of these components, which in turn helps predicting the overall performance of the AMRR system. This work presents modeling methodology along with results from a 1-D transient numerical model of the regenerators of an AMRR capable of removing 2.5 mW at 850 mK at cyclic steadystate.

A paradigmatic 1Dmodel for Brownian motion in a spatially symmetric, periodic system is tackled analytically. Upon application of an external static force F the system's response is an average current which is positive for F < 0 and negative for F > 0 (absolute negative mobility). Under suitable conditions, the system approaches 100% efficiency when working against the external force F.

The correspondence between the steady-state theory of current transfer and scattering theory in a system of coupled tight-binding models of one-dimensional wires is explored. For weak interwire coupling both calculations give nearly identical results, except at singular points associated with band edges. The effect of decoherence in each of these models is studied using a generalization of the Liouville-von Neuman equation suitable for steady-state situations. An example of a single impurity model is studied in detail, leading to a lattice model of scattering off target that affects both potential scattering and decoherence. For an impurity level lying inside the energy band, the transmission coefficient diminishes with increasing dephasing rate, while the opposite holds for impurity energy outside the band. The efficiency of current transfer in the coupled wire system decreases with increasing dephasing. PMID:20707524

In this paper we analyze the steady-state characteristics of bistable semiconductor laser diode (BILD). A simple model for optical output of BILD is obtained using nonlinear rate equations for electron and photon densities. This model emphasizes the physical mechanisms and parameters responsible for the bistability, gives the state equation and explains the main features of BILD. Bistability with a very large hysteresis in P/sub 0/-P/sub 4/ characteristics is a distinctive feature of BILD.

Some volcanoes erupt magma at average rates which are constant over periods of many years, even through this magma may appear in a complex series of eruptions. This constancy of output is tested by construction of a curve of cumulative volume of erupted magma, which is linear for steadystate volcanism, and whose gradient defines the steadystate rate Q/sub s/s. The assumption is made that Q/sub s/s is the rate at which magma is supplied to these polygenetic volcanoes. Five general types of eruptive behavior can be distinguished from the cumulative volume studied. These types are interpreted in terms of a simple model of batches of magma rising buoyantly through the crust and interacting with a small-capacity subvolcanic magma reservoir. Recognition of previous steadystate behavior at a volcano may enable the cumulative volume curve to be used empirically as a constraint on the timing and volume of the next eruption. The steadystatemodel thus has a limited predictive capability. With the exception of Kilauea (O/sub s/s = 4m/sup 3/ s/sup -1/) all the identified steadystate volcanoes have values of Q/sub s/s of a few tenths of one cubic meter per second. These rates are consistent with the minimum flux rates required by theoretical cooling models of batches of magma traversing the crust. The similarity of these Q/sub s/s values of volcanoes (producing basalt, andesite, and dacite magmas) in very different tectonic settings suggests that the common factors of crustal buoyancy forces and the geotherm-controlled cooling rates control the dynamics of magma supply through the crust. Long-term dormancy at active volcanoes may be a manifestation of the steady accumulation of magma in large crustal reservoirs, a process that complements the intermittent periods of steadystate output at the surface. This possibility has several implications, the most important of which is that it provides a constraint on the supply rate of new magma to the bases of plutons.

Apparatus and method for maintaining steadystate compact toroidal plasmas. A compact toroidal plasma is formed by a magnetized coaxial plasma gun and held in close proximity to the gun electrodes by applied magnetic fields or magnetic fields produced by image currents in conducting walls. Voltage supply means maintains a constant potential across the electrodes producing an increasing magnetic helicity which drives the plasma away from a minimum energy state. The plasma globally relaxes to a new minimum energy state, conserving helicity according to Taylor's relaxation hypothesis, and injecting net helicity into the core of the compact toroidal plasma. Controlling the voltage so as to inject net helicity at a predetermined rate based on dissipative processes maintains or increases the compact toroidal plasma in a time averaged steadystate mode.

From the statistical mechanical viewpoint, relaxation of macroscopic systems and response theory rest on a notion of typicality, according to which the behavior of single macroscopic objects is given by appropriate ensembles: ensemble averages of observable quantities represent the measurements performed on single objects, because "almost all" objects share the same fate. In the case of non-dissipative dynamics and relaxation toward equilibrium states, "almost all" is referred to invariant probability distributions that are absolutely continuous with respect to the Lebesgue measure. In other words, the collection of initial micro-states (single systems) that do not follow the ensemble is supposed to constitute a set of vanishing, phase space volume. This approach is problematic in the case of dissipative dynamics and relaxation to nonequilibrium steadystates, because the relevant invariant distributions attribute probability 1 to sets of zero volume, while evolution commonly begins in equilibrium states, i.e., in sets of full phase space volume. We consider the relaxation of classical, thermostatted particle systems to nonequilibrium steadystates. We show that the dynamical condition known as Ω T-mixing is necessary and sufficient for relaxation of ensemble averages to steadystate values. Moreover, we find that the condition known as weak T-mixing applied to smooth observables is sufficient for ensemble relaxation to be independent of the initial ensemble. Lastly, we show that weak T-mixing provides a notion of typicality for dissipative dynamics that is based on the (non-invariant) Lebesgue measure, and that we call physical ergodicity.

From the statistical mechanical viewpoint, relaxation of macroscopic systems and response theory rest on a notion of typicality, according to which the behavior of single macroscopic objects is given by appropriate ensembles: ensemble averages of observable quantities represent the measurements performed on single objects, because " almost all" objects share the same fate. In the case of non-dissipative dynamics and relaxation toward equilibrium states, " almost all" is referred to invariant probability distributions that are absolutely continuous with respect to the Lebesgue measure. In other words, the collection of initial micro-states (single systems) that do not follow the ensemble is supposed to constitute a set of vanishing, phase space volume. This approach is problematic in the case of dissipative dynamics and relaxation to nonequilibrium steadystates, because the relevant invariant distributions attribute probability 1 to sets of zero volume, while evolution commonly begins in equilibrium states, i.e., in sets of full phase space volume. We consider the relaxation of classical, thermostatted particle systems to nonequilibrium steadystates. We show that the dynamical condition known as Ω T-mixing is necessary and sufficient for relaxation of ensemble averages to steadystate values. Moreover, we find that the condition known as weak T-mixing applied to smooth observables is sufficient for ensemble relaxation to be independent of the initial ensemble. Lastly, we show that weak T-mixing provides a notion of typicality for dissipative dynamics that is based on the (non-invariant) Lebesgue measure, and that we call physical ergodicity.

In this thesis, I describe the theoretical development of the superradiant laser, or laser in the extreme bad-cavity regime. In this regime, the cavity decay rate is much greater than the atomic dynamics. The atoms emit photons into the cavity mode superradiantly in steadystate. We develop group-theoretic methods that enable us to exactly solve mesoscopic systems with hundreds of atoms. We demonstrate the synchronization of atomic dipoles in steady-state superradiance. With this synchronized system, we propose conditional Ramsey spectroscopy which allows us to observe Ramsey fringes indefinitely, even in the presence of atomic decoherence. Furthermore, we explore manifestations of synchronization in the quantum realm with two superradiant atomic ensembles. We show that two such ensembles exhibit a dynamical phase transition from two disparate oscillators to quantum phase-locked dynamics. Finally, we study the mechanical eect of the light-atom interaction in the steady-state superradiance. We find efficient many-body cooling of atoms. The work described in this thesis lays the theoretical foundation for the superradiant laser and for a potential future of active optical frequency standards.

This paper is concerned with a compressible viscoelastic fluid model proposed by Öttinger. Although the model has a convex entropy, the Hessian matrix of the entropy does not symmetrize the system of first-order partial differential equations due to the non-conservative terms in the constitutive equation. We show that the corresponding 1Dmodel is symmetrizable hyperbolic and dissipative and satisfies the Kawashima condition. Based on these, we prove the global existence of smooth solutions near equilibrium and justify the compatibility of the model with the Navier-Stokes equations.

A two-dimensional, force-balance magnetic field model is presented. The theoretical existence of a steadystate magnetic field configuration that is force-balanced and consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD is demonstrated. A numerical solution is obtained for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The results are consistent with the convection time sequences reported by Erickson (1985).

For many interesting phenomena in nature, from all life forms to the global climate, the fundamental hypothesis of equilibrium statistical mechanics does not apply. Instead, they are perhaps better characterized by non-equilibrium steadystates, evolving with dynamical rules which violate detailed balance. In particular, such dynamics leads to the existence of non-trivial, persistent probability currents - a principal characteristic of non-equilibrium steadystates. In turn, they give rise to the notion of 'probability angular momentum'. Observable manifestations of such abstract concepts will be illustrated in two distinct contexts: a heterogeneous nonlinear voter model and our ocean heat content. Supported in part by grants from the Bloom Agency (Leeds, UK) and the US National Science Foundation: OCE-1245944. AM acknowledges the support of EPSRC Industrial CASE Studentship, Grant No. EP/L50550X/1.

A theoretical model for stratified epithelium is presented. The viscoelastic properties of the tissue are assumed to be dependent on the spatial distribution of proliferative and differentiated cells. Based on this assumption, a hydrodynamic description of tissue dynamics at the long-wavelength, long-time limit is developed, and the analysis reveals important insights into the dynamics of an epithelium close to its steadystate. When the proliferative cells occupy a thin region close to the basal membrane, the relaxation rate towards the steadystate is enhanced by cell division and cell apoptosis. On the other hand, when the region where proliferative cells reside becomes sufficiently thick, a flow induced by cell apoptosis close to the apical surface enhances small perturbations. This destabilizing mechanism is general for continuous self-renewal multilayered tissues; it could be related to the origin of certain tissue morphology, tumor growth, and the development pattern.

The interplay between turnover or degradation and ribosome loading of messenger RNA (mRNA) is studied theoretically using a stochastic model that is motivated by recent experimental results. Random mRNA degradation affects the statistics of polysomes, i.e., the statistics of the number of ribosomes per mRNA as extracted from cells. Since ribosome loading of newly created mRNA chains requires some time to reach steadystate, a fraction of the extracted mRNA/ribosome complexes does not represent steadystate conditions. As a consequence, the mean ribosome density obtained from the extracted complexes is found to be inversely proportional to the mRNA length. On the other hand, the ribosome density profile shows an exponential decrease along the mRNA for prokaryotes and becomes uniform in eukaryotic cells.

To increase the long-term performance of total joint replacements, finite element analyses of ultra high molecular weight polyethylene (UHMWPE) components have been conducted to predict the effect of load on the stress and strain distributions occurring on and within these components. Early models incorporated the monotonic behavior of UHMWPE without considering the unloading and cyclic loading behavior. However, UHMWPE components undergo cyclic loading during use and at least two wear damage modes (pitting and delamination) are thought to be associated with the fatigue fracture properties of UHMWPE. The objective of this study was to examine the fully reversed uniaxial tension/compression cyclic steadystate stress-strain behavior of UHMWPE as a first step towards developing a cyclic constitutive relationship for UHMWPE. The hypothesis that cycling results in a permanent change in the stress-strain relationship, that is, that the cyclic steadystate represents a new cyclically stabilized state, was examined. It was found that, like other ductile polymers, UHMWPE substantially cyclically softens under fully reversed uniaxial straining. More cyclic softening occurred in tension than in compression. Furthermore, cyclic steadystate was attained, but not cyclic stability. It is suggested that it may be more appropriate to base a material constitutive relationship for UHMWPE for finite element analyses of components upon a cyclically modified stress-strain relationship. PMID:10966018

Over the past two decades, more than 20 mass transfer models have been developed for the sources, sinks, and barriers for volatile and semivolatile organic compounds (VOCs and SVOCs) in the indoor environment. While these models have greatly improved our understanding of VOC and ...

A finite-difference model that simulates three-dimensional flow of groundwater was modified to simulate steady flow of freshwater in a multiple-aquifer system containing freshwater and static saltwater. The two fluids are assumed to be immiscible, with constant but different densities, and are separated by a sharp interface. The interface position computed by the model for a test problem was in good agreement with the analytic solution for this problem. The model was developed to simulate seawater intrusion in coastal aquifers, but it could be used to simulate flow in any aquifer system that is bounded by saltwater. This report describes modifications made to the existing numerical model and the method of locating an interface , and contains a user 's guide for the model. (USGS)

Alkaline-earth-metal-like atoms with ultranarrow optical transitions enable superradiance in steadystate. The emitted light promises to have an unprecedented stability with a linewidth as narrow as a few millihertz. In order to evaluate the potential usefulness of this light source as an ultrastable oscillator in clock and precision metrology applications, it is crucial to understand the noise properties of this device. In this paper, we present a detailed analysis of the intensity fluctuations by means of Monte Carlo simulations and semiclassical approximations. We find that the light exhibits bunching below threshold, is to a good approximation coherent in the superradiant regime, and is chaotic above the second threshold.

An intense, steadystate, low emittance electron beam generator is formed by operating a hollow cathode discharge plasma source at critical levels in combination with an extraction electrode and a target electrode that are operable to extract a beam of fast primary electrons from the plasma source through a negatively biased grid that is critically operated to repel bulk electrons toward the plasma source while allowing the fast primary electrons to move toward the target in the desired beam that can be successfully transported for relatively large distances, such as one or more meters away from the plasma source.

An intense, steadystate, low emittance electron beam generator is formed by operating a hollow cathode discharge plasma source at critical levels in combination with an extraction electrode and a target electrode that are operable to extract a beam of fast primary electrons from the plasma source through a negatively biased grid that is critically operated to repel bulk electrons toward the plasma source while allowing the fast primary electrons to move toward the target in the desired beam that can be successfully transported for relatively large distances, such as one or more meters away from the plasma source. 2 figs.

Two contrasting hypotheses have recently been proposed for the past long-term relation between atmospheric CO2 and the carbonate-silicate geochemical cycle. One approach (Berner, 1990) suggests that CO2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steadystate with respect to tectonically controlled decarbonation reactions. A second approach (Raymo et al., 1988), applied specificlly to the late Cenozoic, suggests a decrease in CO2 caused by an uplift-induced increase in chemical weathering, without regard to the rate of decarbonation. According to the steady-state (first) hypothesis, increased weathering and carbonate sedimentation are generally associated with increasing atmospheric CO2, whereas the uplift (second) hypothesis implies decreasing CO2 under the same conditions. An ocean-atmosphere-sediment model has been used to assess the response of atmospheric CO2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions. Although this assessment is theoretical and cannot yet be related to the geologic record, the model simulations compare steady-state and non-steady-state carbonate-silicate cycle response. The e-fold response time of the 'CO2-weathering' feedback mechanism is between 300 and 400 ka. The response of carbonate sedimentation is much more rapid. These response times provide a measure of the strength of steady-state assumptions, and imply that certain systematic relations are sustained throughout steady-state and non-steady-state scenarios for the carbonate-silicate cycle. The simulations suggest that feedbacks can maintain the system near a steadystate, but that non-steady-state effects may contribute to long-term trends. The steady-state and uplift hypotheses are not necessarily incompatible over time scales of a few million years. ?? 1991.

A computer model to simulate the adiabatic adsorption/desorption process is documented. Developed to predict the performance of desiccant cooling systems, the model has been validated through comparison with experimental data for single-blow adsorption and desorption. A literature review on adsorption analysis, detailed discussions of the adsorption process, and an initial assessment of the potential for performance improvement through advanced component development are included.

A computer model to simulate the adiabatic adsorption/desorption process is documented. Developed to predict the performance of desiccant cooling systems, the model has been validated through comparison with experimental data for single-blow adsorption and desorption. A literature review on adsorption analysis, detailed discussions of the adsorption process, and an initial assessment of the potential for performance improvement through advanced component development are included.

Huntington's disease (HD) cellular pathology is characterised by the aggregation of mutant huntingtin (mHTT) protein into inclusion bodies. The present paper compared the sensitivity of five widely used mHTT antibodies (S830; MW8; EM48; 1C2; ubiquitin) against mice from five commonly used HD mouse models (R6/1; YAC128; HdhQ92; B6 HdhQ150; B6 x129/Ola HdhQ150) at two ages to determine: the most sensitive antibodies for each model; whether mHTT antibody binding differed depending on aggregation stage (diffuse versus frank inclusion); the role of ubiquitin during aggregation as the ubiquitin proteosome system has been implicated in disease development. The models demonstrated unique profiles of antibody binding even when the models varied only by background strain (HdhQ150). MW8 was highly sensitive for detecting frank inclusions in all lines whereas EM48, ubiquitin and 1C2 demonstrated consistent staining in all models irrespective of age or form of mHTT. MW8 and S830 were the most sensitive antibodies with 1C2 the least. Ubiquitin levels were stable for each model regardless of age. Ubiquitin was particularly sensitive in young YAC128 mice that demonstrate an absence of inclusions until ~12 months of age suggesting high affinity to mHTT in its diffuse form. The data indicate that generalisations across models regarding the quantification of aggregations may not be valid and that mHTT antibody binding is unique to the mouse model and sensitive to changes in inclusion development. PMID:27196694

Several new tools, including the Activated Sludge Model No. 2 (ASM No.2) developed by the International Association on Water Quality, are becoming available to analyze the nutrient removal capability of existing wastewater treatment plants (WWTPs). The ASM No. 2 is a potentially inexpensive and effective tool, but its use needs to be evaluated. To solve the differential equations in the model, the computer program Activated Sludge Simulation Program (ASIM 3.0) was used. The model was calibrated using data from the Mauldin Road WWTP, which is a nutrient removal plant. Only 6 of 71 stoichiometric and kinetic parameter values were changed from suggested default values. The stoichiometric and kinetic parameters determined for the Mauldin Road WWTP were then used to develop models for the Lower Reedy, gilder Creek, and Durbin Creek WWTPs. The calibrated model was subsequently confirmed using separate data sets for each WWTP. The model was successfully calibrated and confirmed at the Lower Reedy WWTP. This plant uses high-speed mechanical surface aerators, and it achieves significant phosphorus removal. It was modeled by specifically considering the flow pattern likely to be created by these aerators. Several options to improve the phosphorus removal capability of the Lower Reedy WWTP were evaluated. The simulation results suggested that phosphorus removal performance could be improved by repositioning the mechanical surface aerators to produce a defined anaerobic zone and by providing dissolved oxygen control. The performance of the Durbin Creek and Gilder Creek WWTPs, which use oxidation ditch processes, could not be fully simulated using the model. Potential reasons for this failure are discussed.

Huntington’s disease (HD) cellular pathology is characterised by the aggregation of mutant huntingtin (mHTT) protein into inclusion bodies. The present paper compared the sensitivity of five widely used mHTT antibodies (S830; MW8; EM48; 1C2; ubiquitin) against mice from five commonly used HD mouse models (R6/1; YAC128; HdhQ92; B6 HdhQ150; B6 x129/Ola HdhQ150) at two ages to determine: the most sensitive antibodies for each model; whether mHTT antibody binding differed depending on aggregation stage (diffuse versus frank inclusion); the role of ubiquitin during aggregation as the ubiquitin proteosome system has been implicated in disease development. The models demonstrated unique profiles of antibody binding even when the models varied only by background strain (HdhQ150). MW8 was highly sensitive for detecting frank inclusions in all lines whereas EM48, ubiquitin and 1C2 demonstrated consistent staining in all models irrespective of age or form of mHTT. MW8 and S830 were the most sensitive antibodies with 1C2 the least. Ubiquitin levels were stable for each model regardless of age. Ubiquitin was particularly sensitive in young YAC128 mice that demonstrate an absence of inclusions until ~12 months of age suggesting high affinity to mHTT in its diffuse form. The data indicate that generalisations across models regarding the quantification of aggregations may not be valid and that mHTT antibody binding is unique to the mouse model and sensitive to changes in inclusion development. PMID:27196694

any age. If one accepts that the probability of preserving old crust decreases with increasing age, the few exposures of rocks older than 3.5 Ga should not be surprising. The thickness and compositional differences between Archean and younger lithospheric mantle are not fully understood nor is the role of thicker buoyant mantle in preserving continental crust; these lead to the question of whether the preserved rock record is representative of what formed. It is notable that the oldest known rocks, the ca. 4.0 Ga Acasta Gneisses, are tonalities-granodiorites-granites with evidence for the involvement of even older crust and that the oldest detrital zircons from Australia (ca. 4.0-4.4 Ga) are thought to have been derived from granitoid sources. The global Hf and Nd isotope databases are compatible with both depleted and enriched sources being present from at least 4.0 Ga to the present and that the lack of evolution of the MORB source or depleted mantle is due to recycling of continental crust throughout earth history. Using examples from the Slave Province and southern Africa, we argue that Armstrong's concept of steadystate crustal growth and recycling via plate tectonics still best explains the modern geological and geochemical data.

The balance of stable and decaying tracers was incorporated into a latitude-depth ocean circulation model which resolves the major ocean basin and is coupled to an atmospheric energy balance model. The modern distribution of radiocarbon and the analysis of artificial color tracers enabled the census of the deep water masses. We show that good agreement with the observation can be achieved if the surface forcing is modified. The same process could also account for long-term, large-scale changes of the global thermohaline circulation. Uptake rates of carbon are investigated using an inorganic carbon cycle model and performing 2 {times} CO{sub 2}-experiments. We prescribe the industrial evolution of pCO{sub 2} in the atmosphere from 1792 to 1988 and calculate the total flux of carbon into the world ocean. Results are in good agreement with two recent 3-dimensional model simulation. First results using an organic carbon cycle in this model are presented. Changes in the hydrological cycle can stabilize the thermohaline circulation in the Atlantic and enable simulation of climate events resembling the Younger Dryas. By adding the balance of radiocarbon the evolution of its atmospheric concentration is studied during rapid changes of deep ocean ventilation. A resumption of ventilation creates a rapid decrease of atmospheric radiocarbon which is able to mask the natural decay.

The authors have completed the studies using the inorganic carbon cycle in the zonally averaged ocean circulation model to calculate anthropogenic uptake of CO{sub 2} and bomb radiocarbon. While the results are in broad agreement with previous studies, the authors have learned that horizontal mixing processes due to gyre circulation are important for transient tracer experiments over a few decades. Using the inorganic carbon cycle model the authors have started to look at the distributions of {delta}{sup 13}C in the ocean. The model is able to reproduce faithfully the air-sea fractionation of {delta}{sup 13}C. The effect of changing sea surface temperature in the middle and low latitudes of the world ocean on {rho}CO{sub 2}{sup atm} is studied in this model and compared to the organic carbon cycle model of the Hamburg group. They find significant differences in sensitivity and are in the process of investigating possible reasons. Incorporation of the organic component is still ongoing. In the present version the surface concentrations of phosphate are still too high indicating strong upwelling.

We have completed the studies using the inorganic carbon cycle in the zonally averaged ocean circulation model to calculate anthropogenic uptake of CO, and bomb radiocarbon. While our results are in broad agreement with previous studies, we have learned that horizontal mixing processes due to gyre circulation are important for transient tracer experiments over a few decades. These findings are in press. Using the inorganic carbon cycle model we have started to look at the distributions of {delta}{sup 13}C in the ocean. The model is able to reproduce faithfully the air-sea fractionation of {delta}{sup 13}C. The effect of changing sea surface temperature in the middle and low latitudes of the world ocean on pCO{sub 2{sup atm}} is studied in this model and compared to the organic carbon cycle model of the Hamburg group. We find significant differences in sensitivity and are in the process of investigating possible reasons. Incorporation of the organic component is still ongoing. In the present version the surface concentrations of phosphate are still too high indicating strong upwelling.

The deep circulation model developed by Wright and Stocker has been used to represent the latitude-depth distributions of temperature, salinity, radiocarbon and ``color`` tracers in the Pacific, Atlantic and Indian Oceans. Restoring temperature and salinity to observed surface data the model shows a global thermohaline circulation where deep water is formed in the North Atlantic and in the Southern Ocean. A parameter study reveals that the high-latitude surface salinity determines the composition of deep water and its flow in the global ocean. Increasing Southern Ocean surface salinity by 0.4 ppt the circulation changes from a present-day mode where North Atlantic Deep Water is one where Antarctic Bottom Water is dominant. An inorganic carbon cycle with surface carbonate chemistry is included, and gas exchange is parameterized in terms of pCO{sub 2} differences. Pre- industrial conditions are achieved by adjusting the basin-mean alkalinity. A classical 2{times}CO{sub 2} experiment yields the intrinsic time scales for carbon uptake of the ocean; they agree with those obtained from simple box models or 3-dimensional ocean general circulation models. Using the estimated industrial anthropogenic input of CO{sub 2} into the atmosphere the model requires, consistent with other model studies, an additional carbon flux to match the observed increase of atmospheric pCO{sub 2}. We use more realistic surface boundary conditions which reduce sensitivity to freshwater discharges into the ocean. In a glacial-to-interglacial experiment rapid transitions of the deep circulation between two different states occur in conjunction with a severe reduction of the meridional heat flux and sea surface temperature during peak melting. After the melting the conveyor belt circulation restarts.

A computer program has been developed as part of the U.S. Geological Survey's national program of Regional Aquifer System Analysis (RASA) that generates input to ground-water flow models to enable them to simulate variable-density ground-water flow. Information required for the program's operation is: aquifer elevation, thickness, and ground-water density. Included in the report is a computer program for calculating ground-water density from aquifer depth, temperature, and dissolved solids concentration. The 60-page report describes the theoretical development and documents two FORTRAN programs used to generate the necessary flow-model input. An example for a symmetrical basin is fully worked out.

A digital model calibrated to conditions in Clear Creek, Monroe County, IN, was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The Winston Thomas wastewater-treatment facility is the only point-source waste load affecting the modeled reach of Clear Creek. A new waste-water-treatment facility under construction at Dillman Road (river mile 13.78) will replace the Winston Thomas wastewater-treatment facility (river mile 16.96) in 1980. Natural streamflow during the summer and annual 7-day, 10-year low flow is zero, so no benefit from dilution is provided. The model indicates that ammonia-nitrogen toxicity is the most significant factor affecting the stream water quality during summer and winter low flows. The ammonia-nitrogen concentration of the wastewater effluent exceeds the maximum total ammonia-nitrogen concentration of 2.5 milligrams per liter for summer months (June through August) and 4.0 milligrams per liter for winter months (November through March) required for Indiana streams. Nitrification, benthic-oxygen demand, and algal respiration were the most significant factors affecting the dissolved-oxygen concentration in Clear Creek during the model calibration. Nitrification should not significantly affect the dissolved-oxygen concentration in Clear Creek during summer low flows when the ammonia-nitrogen toxicity standards are met. (USGS)

Naturally occurring gravity currents include events such as air flowing through an open front door, a volcanic eruption's pyroclastic flow down a mountainside, and the spread of the Bhopal disaster's methyl isocyanate gas. Gravity currents typically have a small height-to-distance ratio. Plastic models were designed and constructed with a…

A digital model calibrated to conditions in the Mississinewa River, Grant County, IN was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The hydrology of the Mississinewa River downstream from Gas City is controlled primarily by two factors; low slopes, typical of the Tipton Till Plain, and a 10-foot dam at river mile 35.9, in Marion. All point-source waste loads affecting the modeled segment of the Mississinewa River are in the four incorporated municipalities of Fairmount, Jonesboro, Gas City, and Marion, in a primarily agricultural area. Model simulations indicate that algal photosynthesis and nitrification are the most significant factors affecting the dissolved-oxygen concentration in the Mississinewa River during summer low flows. Natural reaeration without photosynthesis, is not sufficient to maintain an average dissolved-oxygen concentration of at least 5 milligrams per liter in the stream, the State 's water-quality standard. Projected carbonaceous and nitrogenous biochemical-oxygen demand loads, from the Indiana State Board of Health, for Owens, Illinois, Inc., and the Gas City and Marion wastewater-treatment facility will result in violations of the instream dissolved-oxygen standard. Fairmount and Jonesboro, because of their distance from the Mississinewa, do not significantly affect the water quality of the modeled segment. The model also indicates that, during winter low flows, ammonia toxicity, rather than dissolved oxygen is the limiting water-quality criterion in the Mississinewa River downstream from the Gas City wastewater-treatment facility. (USGS)

Steadystate groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented, using the Dupuit approximation, by an ordinary differential equation of the Abel type y(x) · y'(x) + a · y(x) + x = 0, whose analytical solution is derived in this work. This article first investigates the case of zero saturated thickness at the upstream boundary, a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary. A variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary. This variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer, the latter being on sloping terrain in this instance. Analytical solutions for the phreatic surface's steadystate geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface. These solutions are of practical interest in drainage studies, slope stability, and runoff formation investigations. It is shown that the flow factor a = -? tan β (where K, N, and tan β are the hydraulic conductivity, vertical recharge, and aquifer slope, respectively) has a commanding role on the phreatic surface's solutions. Two computational examples illustrate the implementation of this article's results.

Steadystate groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented, using the Dupuit approximation, by an ordinary differential equation of the Abel type y(x) . y'(x) + a . y(x) + x = 0, whose analytical solution is derived in this work. This article first investigates the case of zero saturated thickness at the upstream boundary, a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary. A variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary. This variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer, the latter being on sloping terrain in this instance. Analytical solutions for the phreatic surface's steadystate geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface. These solutions are of practical interest in drainage studies, slope stability, and runoff formation investigations. It is shown that the flow factor a = -$\\sqrt{{\\rm K}/{\\rm N} tan β (where K, N, and tan β are the hydraulic conductivity, vertical recharge, and aquifer slope, respectively) has a commanding role on the phreatic surface's solutions. Two computational examples illustrate the implementation of this article's results.

Chilliwack River is typical of many Cordilleran valley river systems that have undergone dramatic Holocene degradation of valley fills that built up over the course of Pleistocene glaciation. Downstream controls on base level, mainly blockage of valleys by glaciers, led to aggradation of significant glaciofluvial and glaciolacustrine valley fills and fan deposits, subsequently incised by fluvial action. Models of such large-scale, long-term degradation present a number of important challenges since the evolution of model parameters, such as the rate of bedload transport and grain size characteristics, are governed by the nature of the deposit. Sediment sampling in the Chilliwack Valley reveals a complex sequence of very coarse to fine textural modes. We present a 1-D numerical morphodynamic model for the river-floodplain system tailored to conditions in the valley. The model is adapted to dynamically adjust channel width to optimize sediment transporting capacity and to integrate relict valley fill material as the channel incises through valley deposits. Sensitivity to model parameters is studied using four principal criteria: profile concavity, rate of downstream grain size fining, bed surface sand content, and the timescale to equilibrium. Model results indicate that rates of abrasion and coarsening of the grain size distributions exert the strongest controls on all of the interrelated model performance criteria. While there are a number of difficulties in satisfying all model criteria simultaneously, results indicate that 1-Dmodels of valley bottom sedimentary systems can provide a suitable framework for integrating results from sediment budget studies and chronologies of sediment evacuation established from dating.

A digital model calibrated to conditions in East Fork White River, Bartholomew County, IN, was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The model indicates that benthic-oxygen demand and the headwater concentrations of carbonaceous biochemical-oxygen demand, nitrogenous biochemical-oxygen demand, and dissolved oxygen are the most significant factors affecting the dissolved-oxygen concentration of East Fork White River downstream from the Columbus wastewater-treatment facility. The effect of effluent from the facility on the water quality of East Fork White River was minimal. The model also indicates that, with a benthic-oxygen demand of approximately 0.65 gram per square meter per day, the stream has no additional waste-load assimilative capacity during summer low flows. Regardless of the quality of the Columbus wastewater effluent, the minimum 24-hour average dissolved-oxygen concentration of at least 5 milligrams per liter, the State 's water-quality standard for streams, would not be met. Ammonia toxicity is not a limiting water-quality criterion during summer and winter low flows. During winter low flows, the current carbonaceous biochemical-oxygen demand limits for the Columbus wastewater-treatment facility will not result in violations of the in-stream dissolved-oxygen standard. (USGS)

The Indiana State Board of Health is developing a State water-quality management plan that includes establishing limits for wastewater effluents discharged into Indiana streams. A digital model calibrated to conditions in Silver Creek was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. Effluents from the Sellersburg and Clarksville-North wastewater-treatment facilities are the only point-source waste loads that significantly affect the water quality in the modeled segment of Silver Creek. Model simulations indicate that nitrification is the most significant factor affecting the dissolved-oxygen concentration in Silver Creek during summer and winter low flows. Natural streamflow in Silver Creek during the summer and annual 7-day, 10-year low flow is zero, so no benefit from dilution is provided. Present ammonia-nitrogen and dissolved-oxygen concentrations of effluent from the Sellersburg and Clarksville-North wastewater-treatment facilities will violate current Indiana water-quality standards for ammonia toxicity and dissolved oxygen during summer and winter low flows. The current biochemical-oxygen demand limits for the Sellersburg and Clarksville-North wastewater-treatment facilities are not sufficient to maintain an average dissolved-oxygen concentration of at least 5 milligrams per liter, the State 's water-quality standard for streams. Calculations of the stream 's assimilative capacity indicate that Silver Creek cannot assimilate additional waste loadings and meet current Indiana water-quality standards. (Kosco-USGS)

A digital model calibrated to conditions in Sand Creek near Greensburg, Ind., was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The only point-source waste load affecting Sand Creek in the vicinity of Greensburg is the Greensburg wastewater-treatment facility. Non-point, unrecorded waste loads seemed to be significant during three water-quality surveys done by the Indiana State Board of Health. Natural streamflow in Sand Creek during the summer and annual 7-day, 10-year low flow is zero so no benefit from dilution is provided. Effluent ammonia-nitrogen concentrations from the Greensburg wastewater-treatment facility will not meet Indiana water-quality standards during summer and winter low flows. To meet the water-quality standard the wastewater-effluent would be limited to a maximum total ammonia-nitrogen concentration of 2.5 mg/l for summer months (June through August) and 4.0 mg/l for winter months (November through March). Model simulations indicate that benthic-oxygen demand, nitrification, and the dissolved-oxygen concentration of the wastewater effluent are the most significant factors affecting the in-stream dissolved-oxygen concentration during summer low flows. The model predicts that with a benthic-oxygen demand of 1.5 grams per square meter per day at 20C the stream has no additional waste-load assimilative capacity. Present carbonaceous biochemical-oxygen demand loads from the Greensburg wastewater-treatment facility will not result in violations of the in-stream dissolved-oxygen standard (5 mg/l) during winter low flows. (Kosco-USGS)

A digital model calibrated to conditions in Cedar Creek was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The model indicates that the dissolved-oxygen concentration of the Auburn wastewater effluent and nitrification are the most significant factors affecting the dissolved-oxygen concentration in Cedar Creek during summer low flows. The observed dissolved-oxygen concentration of the Auburn wastewater effluent was low and averaged 30 percent of saturation. Projected nitrogenous biochemical-oxygen demand loads, from the Indiana State Board of Health, for the Auburn and Waterloo wastewater-treatment facilities will result in violations of the current instream dissolved-oxygen standard (5 mg/l), even with an effluent dissolved-oxygen concentration of 80 percent saturation. Natural streamflow for Cedar Creek upstream from the confluence of Willow and Little Cedar Creeks is small compared with the waste discharge, so benefits of dilution for Waterloo and Auburn are minimal. The model also indicates that, during winter low flows, ammonia toxicity, rather than dissolved oxygen, is the limiting water-quality criterion in the reach of Cedar Creek downstream from the wastewater-treatment facility at Auburn and the confluence of Garrett ditch. Ammonia-nitrogen concentrations predicted for 1978 through 2000 downstream from the Waterloo wastewater-treatment facility do not exceed Indiana water-quality standards for streams. Calculations of the stream 's assimilative capacity indicate that future waste discharge in the Cedar Creek basin will be limited to the reaches between the Auburn wastewater-treatment facility and County Road 68. (Kosco-USGS)

The Indiana State Board of Health is developing a water-quality management plan that includes establishing limits for wastewater effluents discharged into Indiana streams. A digital model calibrated to conditions in Wildcat Creek was used to predict alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The model indicates that benthic-oxygen demand is the most significant factor affecting the dissolved-oxygen concentrations in Wildcat Creek during summer low flows. The Indiana stream dissolved-oxygen standard should not be violated if the Kokomo wastewater-treatment facility meets its current National Pollution Discharge Elimination System permit restrictions (average monthly 5-day biochemical-oxygen demand of 5 milligrams per liter and maximum weekly 5-day biochemical-oxygen demand of 7.5 milligrams per liter) and benthic-oxygen demand becomes negligible. Ammonia-nitrogen toxicity may also be a water-quality limitation in Wildcat Creek. Ammonia-nitrogen waste loads for the Kokomo wastewater-treatment facility, projected by the Indiana State Board of Health, will result in stream ammonia-nitrogen concentrations that exceed the State standard (2.5 milligrams per liter during summer months and 4.0 milligrams per liter during winter months). (Kosco-USGS)

The Indiana State Board of Health is developing a State water-quality management plan that includes establishing limits for wastewater effluents discharged into Indiana streams. A digital model calibrated to conditions in South Fork Wildcat Creek was used to predict alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. Natural streamflow during the 7-day, 10-year low flow is zero, so no benefit from dilution is provided. The Indiana State Board of Health 's projected ammonia-nitrogen concentration for the Frankfort wastewater-treatment facility will violate the instream total ammonia-nitrogen standard of 2.5 mg/l and 4.0 mg/l during summer and winter low flows, respectively. The model indicates that nitrification and algal respiration were significant factors affecting the dissolved-oxygen dynamics of South Fork Wildcat Creek during two water-quality surveys. Stream water quality during the two water-quality surveys was degraded by the discharge of wastewater receiving only primary treatment. Benthic deposits resulting from this wastewater discharge seem to exert a considerable oxygen demand. The discharge of partially treated wastewater should be eliminated when a new wastewater-treatment facility becomes operational in mid-1979. Therefore, benthic-oxygen demand due to benthic deposits should become negligible at that time.

Each year, hundreds of thousands of aortic and mitral heart valves are replaced with prosthetic valves. In efforts to develop a valve that does not require lifelong anticoagulation therapy, previous experimental research has been devoted to analyzing the hemodynamics of various heart valve designs, limited to the flow up to only 2 diameters downstream of the valve. Two-component, two-dimensional (2C-2D) particle image velocimetry (PIV) was used in this study to examine secondary flow velocity fields in a curved tube modeling an aorta at five locations (0-, 45-, 90-, 135-, 180-degrees). A bileaflet valve, opened to 30-, 45-, and 59-degrees, and one (no-valve) baseline condition were examined under three steady flow inflows (Re = 218, 429, 634). In particular, variations in the two-dimensional turbulent shear stresses at each cross sectional plane were analyzed. The results suggest that bileaflet valves in the aortic model produce significant turbulence and vorticity up to 5.5 downstream diameters, i.e. up to the 90-degrees location. Expanding this research towards aortic heart valve hemodynamics highlights a need for additional studies extending beyond the typical few diameters downstream to fully characterize valvular function. Supported by the NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.

This characterization and modeling study of dispersive tidal plume of brine discharge from reverse osmosis (RO) desalination system is a part of the Environmental Assessment (EA) for a new reverse osmosis system in the Coral Bay, St. John, USVI (US Virgin Island). Main foci are on developing the tidal longitudinal (perpendicular to the shoreline) and lateral (parallel to the shoreline) dispersion coefficients and subsequently characterize dispersion and mixing characterization of the negatively buoyant brine discharge plume from the proposed reverse osmosis plant to evaluate the level of salinity variations in the nearshore mixing plume in regard to existing coral reef ecosystem. An in situ dye study was conducted by a marine biologist for this purpose to estimate brine discharge plume dispersion coefficients under oscillatory tidal transport and fate flux for current and proposed plant configuration. Additional tidal and surface runoff hydrologic data, bathymetric data and brine discharge characteristics in the vicinity of the brine discharge location are reflected in this study. With estimated dispersion coefficients, eighteen brine discharge scenarios were evaluated to model anticipated dispersive characteristics under varying operational conditions and ambient tidal current conditions for average measured salinity of 33.27 PSU in loco as well as a standard 35 PSU for typical nearshore water salinity variations. Modeling results indicated that the dispersive tidal plume of design brine discharge from reverse osmosis (RO) desalination system at a discharge of 150,000 gpd would raise salinity no higher than 0.0123 PSU in receiving nearshore estuarine water (Maximum concentration at the segment 3 = 33.2822 PSU at Δt = 12 hrs and 24 hrs in diurnal tidal cycle under when the brine discharge with Base+25% concentration, 81.25 PSU at brine discharge rate of 0.0066 m3/sec, and with a minimum direct overland flow efflux at 0.003 m3/sec - this is a "worst-case" operating

Uranium carbide (UC) has long been considered a potential alternative to uranium dioxide (UO2) fuel, especially in the context of Gen IV gas-cooled reactors. It has shown promise because of its high uranium density, good irradiation stability, and especially high thermal conductivity. Despite its many benefits, UC is known to swell at a rate twice that of UO2. However, the swelling phenomenon is not well understood, and we are limited to a weak empirical understanding of the swelling mechanism. One suggested cladding for UC is silicon carbide (SiC), a ceramic that demonstrates a number of desirable properties. Among them are an increased corrosion resistance, high mechanical strength, and irradiation stability. However, with increased temperatures, SiC exhibits an extremely brittle nature. The brittle behavior of SiC is not fully understood and thus it is unknown how SiC would respond to the added stress of a swelling UC fuel. To better understand the interaction between these advanced materials, each has been implemented into FRAPCON, the preferred fuel performance code of the Nuclear Regulatory Commission (NRC); additionally, the material properties for a helium coolant have been incorporated. The implementation of UC within FRAPCON required the development of material models that described not only the thermophysical properties of UC, such as thermal conductivity and thermal expansion, but also models for the swelling, densification, and fission gas release associated with the fuel's irradiation behavior. This research is intended to supplement ongoing analysis of the performance and behavior of uranium carbide and silicon carbide in a helium-cooled reactor.

The Main Endeavour Field (MEF) on the Juan de Fuca Ridge consists of a large number of chimney structures occupying an area approximately 400 m x 150 m along the ridge axis. For nearly a decade, the MEF exhibited quasi-steady north-south trending spatial gradients of both temperature and salinity. We have constructed 2-D across-axis numerical models of two-phase flow using the code FISHES to investigate possible causes for this variation. We considered the effect of bottom boundary temperature and both a homogeneous permeability structure and a geometry incorporating a more-permeable layer 2A. From these model results we argue that such a trend is more likely to be the result of heterogeneous permeability structure of the shallow oceanic crust than a result of bottom boundary temperature variations. After a magmatic event in 1999, this trend was disrupted; and thermal data using the Autonomous Benthic Explorer (ABE) indicates that there has been a significant decline in the heat output from a value of approximately 450 MW in 2000 to approximately 300 MW in 2004. In the southern part of the vent field, vent salinities have also increased from values well below those of seawater to values close to seawater. We therefore extend our investigation to include the effect of a temporally-decaying basal heat flow, which may result from cooling, crystallizing magma chamber, on the system. Our aim is to determine whether such a phenomenon could cause the observed rapid decline of heat flow and changes in vent salinity at the MEF. We find that the thermal inertia in the system is such that changes in basal heat flow would be difficult to detect in the given time frame, if magma replenishment ceased following the 1999 magmatic event. The time delay between changes in bottom conditions and the observed decay in observed heat output suggests that the 1999 event represented a small replenishment event and that the AMC may have begun cooling some time before that. Moreover, because

A digital model calibrated to conditions in the Wabash River in Huntington County, Ind., was used to predict alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditons, summer and winter low flows. The major point-source waste load affecting the Wabash River in Huntington County is the Huntington wastewater-treatment facility. The most significnt factor potentially affecting the dissolved-oxygen concentration during summer low flows is nitrification. However, nitrification should not be a limiting factor on the allowable nitrogenous and carbonaceous waste loads for the Huntington wastewater-treatment facility during summer low flows if the ammonia-nitrogen toxicity standard for Indiana streams is met. The disolved-oxygen standard for Indiana stream, an average of 5.0 milligrams per liter, should be met during summer and winter low flows if the National Pollution Discharge Elimination System 's 5-day, carbonaceous biochemical-oxygen demands of a monthly average concentration of 30 milligrams per liter and a maximum weekly average of 45 milligrams per liter are not exceeded.

A digital computer model calibrated to observe stream conditions was used to evaluate water quality in West Fork Blue River, Washington County, IN. Instream dissolved-oxygen concentration averaged 96.5% of saturation at selected sites on West Fork Blue River during two 24-hour summer surveys. This high dissolved-oxygen concentration reflects small carbonaceous and nitrogenous waste loads; adequate dilution of waste by the stream; and natural reaeration. Nonpoint source waste loads accounted for an average of 53.2% of the total carbonaceous biochemical-oxygen demand and 90.2% of the nitrogenous biochemical-oxygen demand. Waste-load assimilation was studiedfor critical summer and winter low flows. Natural streamflow for these conditions was zero, so no benefit from dilution was provided. The projected stream reaeration capacity was not sufficient to maintain the minimum daily dissolved-oxygen concentration (5 milligrams per liter) in the stream with current waste-discharge restrictions. During winter low flow, ammonia toxicity, rather than dissolved-oxygen concentration, was the limiting water-quality criterion downstream from the Salem wastewater-treatment facility. (USGS)

A digital model calibrated to conditions in Little Laughery Creek triutary and Little Laughery Creek, Ripley and Franklin Counties, Ind., was used to predict alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. Natural streamflow during the summer and annual 7-day, 10-year low flow is zero. Headwater flow upstream from the wastewater-treatment facilities consists solely of process cooling water from an industrial discharger. This flow is usually less than 0.5 cubic foot per second. Consequently, benefits from dilution are minimal. As a result, current and projected ammonia-nitrogen concentrations from the municipal discharges will result in in-stream ammonia-nitrogen concentrations that exceed the Indiana ammonia-nitrogen toxicity standards (maximum stream ammonia-nitrogen concentrations of 2.5 and 4.0 milligrams per liter during summer and winter low flows, respectively). Benthic-oxygen demand is probably the most significant factor affecting Little Laughery Creek and is probably responsible for the in-stream dissolved-oxygen concentration being less than the Indiana stream dissolved-oxygen standard (5.0 milligrams per liter) during two water-quality surveys. After municipal dischargers complete advanced waste-treatment facilities, benthic-oxygen demand should be less significant in the stream dissolved-oxygen dynamics. (USGS)

As highly promising coolant for new generation nuclear reactors, liquid Lead-Bismuth Eutectic has been extensively worldwide investigated. With high expectation about this advanced coolant, a multi-national systematic study on LBE was proposed in 2007, which covers benchmarking of thermal hydraulic prediction models for Lead-Alloy Cooled Advanced Nuclear Energy System (LACANES). This international collaboration has been organized by OECD/NEA, and nine organizations - ENEA, ERSE, GIDROPRESS, IAEA, IPPE, KIT/IKET, KIT/INR, NUTRECK, and RRC KI - contribute their efforts to LACANES benchmarking. To produce experimental data for LACANES benchmarking, thermal-hydraulic tests were conducted by using a 12-m tall LBE integral test facility, named as Heavy Eutectic liquid metal loop for integral test of Operability and Safety of PEACER (HELIOS) which has been constructed in 2005 at the Seoul National University in the Republic of Korea. LACANES benchmark campaigns consist of a forced convection (phase-I) and a natural circulation (phase-II). In the forced convection case, the predictions of pressure losses based on handbook correlations and that obtained by Computational Fluid Dynamics code simulation were compared with the measured data for various components of the HELIOS test facility. Based on comparative analyses of the predictions and the measured data, recommendations for the prediction methods of a pressure loss in LACANES were obtained. In this paper, results for the forced convection case (phase-I) of LACANES benchmarking are described.

The Indiana State Board of Health is developing a State water-quality plan that includes establishing limits for wastewater effluents discharged into Indiana streams. A digital model calibrated to conditions in Duck Creek was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The major point-source waste load affecting Duck Creek is the Elwood wastewater-treatment facility. Natural streamflow during the low flow is zero, so no benefit from dilution is provided. Natural reaeration at the low-flow condition (approximately 3 cubic feet per second), also low, is estimated to be less than 1 per day (base e at 20 Celsius). Consequently, the wasteload assimilative capacity of the stream is low. Effluent ammonia-nitrogen concentrations, projected by the Indiana State Board of Health, will result in stream ammonia-nitrogen concentrations that exceed the State ammonia-nitrogen toxicity standards (2.5 milligrams per liter from April to October and 4.0 milligrams per liter from November through March). The projected effluent ammonia-nitrogen load will also result in the present Indiana stream dissolved-oxygen standard (5.0 milligrams per liter) not being met. Benthic-oxygen demand may also affect stream water quality. During the summer low-flow, a benthic-oxygen demand of only 0.6 gram per square meter per day would utilize all the streams 's available assimilative capacity. (USGS)

A steadystatemodel, constrained by a number of measured quantities, was used to derive peroxy radical levels for the conditions of the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign. The analysis is made using data collected aboard the NCAR/NSF C-130 aircraft from February through May 2000 at latitudes from 40° to 85°N, and at altitudes from the surface to 7.6 km. HO2 + RO2 radical concentrations were measured during the experiment, which are compared with model results over the domain of the study showing good agreement on the average. Average measurement/model ratios are 1.04 (σ = 0.73) and 0.96 (σ = 0.52) for the MLB and HLB, respectively. Budgets of total peroxy radical levels as well as of individual free radical members were constructed, which reveal interesting differences compared to studies at lower latitudes. The midlatitude part of the study region is a significant net source of ozone, while the high latitudes constitute a small net sink leading to the hypothesis that transport from the middle latitudes can explain the observed increase in ozone in the high latitudes. Radical reservoir species concentrations are modeled and compared with the observations. For most conditions, the model does a good job of reproducing the formaldehyde observations, but the peroxide observations are significantly less than steadystate for this study. Photostationary state (PSS) derived total peroxy radical levels and NO/NO2 ratios are compared with the measurements and the model; PSS-derived results are higher than observations or the steadystatemodel at low NO concentrations.

The U.S. Geological Survey, in cooperation with the Department of Energy and other Federal, State, and local agencies, is evaluating the hydrogeologic characteristics of the Death Valley regional ground-water flow system. The ground-water flow system covers an area of about 100,000 square kilometers from latitude 35? to 38?15' North to longitude 115? to 118? West, with the flow system proper comprising about 45,000 square kilometers. The Death Valley regional ground-water flow system is one of the larger flow systems within the Southwestern United States and includes in its boundaries the Nevada Test Site, Yucca Mountain, and much of Death Valley. Part of this study includes the construction of a three-dimensional hydrogeologic framework model to serve as the foundation for the development of a steady-state regional ground-water flow model. The digital framework model provides a computer-based description of the geometry and composition of the hydrogeologic units that control regional flow. The framework model of the region was constructed by merging two previous framework models constructed for the Yucca Mountain Project and the Environmental Restoration Program Underground Test Area studies at the Nevada Test Site. The hydrologic characteristics of the region result from a currently arid climate and complex geology. Interbasinal regional ground-water flow occurs through a thick carbonate-rock sequence of Paleozoic age, a locally thick volcanic-rock sequence of Tertiary age, and basin-fill alluvium of Tertiary and Quaternary age. Throughout the system, deep and shallow ground-water flow may be controlled by extensive and pervasive regional and local faults and fractures. The framework model was constructed using data from several sources to define the geometry of the regional hydrogeologic units. These data sources include (1) a 1:250,000-scale hydrogeologic-map compilation of the region; (2) regional-scale geologic cross sections; (3) borehole information, and (4

At the Institut fuer Raumfahrtsysteme (IRS) rotation symmetric magnetoplasmadynamic thrusters with self induced magnetic fields are investigated at high current levels in a steadystate operation mode. MPD thrusters with different geometrics were compared, and the influence of mass flow rate and power input on the operating conditions of the thrusters explored. By optical and probe measurements, a systematic investigation of the plasma plume has been started. The investigation of the various instabilities of the arc and the plasma flow appearing at high power levels was continued. The computer code development for the geometry optimization of continuous self-field MPD thrusters, running with argon, was modified by considering higher degrees of ionization, which showed better agreement with the experiment.

To examine the limitations of one-dimensional (1D) solar cell modeling, 3D SPICE-based modeling is used to examine in detail the validity of the 1D assumptions as a function of sheet resistance for a model cell. The internal voltages and current densities produced by this modeling give additional insight into the differences between the 1D and 3D models.

The velocity fluctuations and the local particle concentration of a particle suspension exhibiting steadystate sedimentation in a fluidized bed are determined as a function of height along the particle column. Both the velocity fluctuations and the particle volume fraction are found to strongly depend on height. We account for the stability of the bed by a simple model evoking a flux balance. Velocity fluctuations driving a downward particle flux are compensated by an upward particle flux stemming from an excess flow velocity due to the concentration gradient of the system.

We first present nonadiabatic path integral which is exact formulation of quantum dynamics in nonadiabatic systems. Then, by applying the stationary phase approximations to the nonadiabatic path integral, a semiclassical quantization condition, i.e., quantum-classical correspondence, for steadystates of nonadiabatic systems is presented as a nonadiabatic trace formula. The present quantum-classical correspondence indicates that a set of primitive hopping periodic orbits, which are invariant under time evolution in the phase space of the slow degree of freedom, should be quantized. The semiclassical quantization is then applied to a simple nonadiabatic model and accurately reproduces exact quantum energy levels.

The evolution of mountain ranges to steadystate is an important concept in the study of the interrelationships between climate, mountain building and topography. The young and active Taiwan orogeny situated in the western pacific typhoon belt has often been regarded as the type locality of a steadystate orogeny, and an ideal case study for tectonic and climatic geomorphology. One prediction of the steady-state theory applied to mountains is the attainment of a constant sediment flux. Our aim in the present study is to estimate the material flux out of the Taiwan orogeny through its evolution. To do so, we have studied the basin wide sedimentary facies distribution at five key stratigraphic horizons to construct detailed paleogeographic maps that include paleobathymetric information and sediment feeding systems. The maps highlight the complicated basin-wide dynamics of sediment dispersal within an evolving foreland basin. The basin physiography changed very little from the middle Miocene (around 12.5 Ma) to the late Pliocene (around 3 Ma); the paleoenvironments were essentially maintained from the passive margin to the foreland basin stage. At 3 Ma, during deposition of the mud-dominated Chinshui Shale, the main depositional basin started to widen and deepen. This clearly marks the increased subsidence associated with the approach of the growing orogen to the east. The basin started to become filled in the late early Pleistocene when a shallow marine wedge in front of the growing orogen initiated to propagate towards the south. We use Dionisos, a forward stratigraphic model, to simulate the evolution of the Taiwan foreland basin in terms of sediment flux (in and out of the basin) towards steadystate. We constrain the model with our paleogeographic and sedimentary reconstructions. As an initial input data we utilize the paleoenvironmental maps and a primary sediment supply from the hinterland (topography). The model enables us to look at the long-term basin

A 1-D Fast Current Quench (FCQ) model is developed to study current evolution and runaway electron suppression under massive density increase. The model consists of coupled toroidal electric field and energy equations, and it is solved numerically for DIII-D and ITER operating conditions. Simulation results suggest that fast shutdown by D2 liquid jet/pellet injection is in principle achievable for the desired plasma cooling time (˜15 ms for DIII-D and ˜50 ms for ITER) under ˜150x or higher densification. The current density and pressure profile are practically unaltered during the initial phase of jet propagation when dilution cooling dominates. With subsequent radiation cooling, the densified discharge enters the strongly collisional regime where Pfirsch-Schluter thermal diffusion can inhibit current contraction on the magnetic axis. Often the 1/1 kink instability, addressed by Kadomtsev's magnetic reconnection model, can be prevented. Our results are compared with NIMROD simulations in which the plasma is suddenly densified by ˜100x and experiences instantaneous dilution cooling, allowing for use of actual (lower) Lundquist numbers.

Under static conditions, a system satisfying detailed balance generically relaxes to an equilibrium state in which there are no currents. To generate persistent currents, either detailed balance must be broken or the system must be driven in a time-dependent manner. A stationary system that violates detailed balance evolves to a nonequilibrium steadystate (NESS) characterized by fixed currents. Conversely, a system that satisfies instantaneous detailed balance but is driven by the time-periodic variation of external parameters—also known as a stochastic pump (SP)—reaches a periodic state with nonvanishing currents. In both cases, these currents are maintained at the cost of entropy production. Are these two paradigmatic scenarios effectively equivalent? For discrete-state systems, we establish a mapping between nonequilibrium stationary states and stochastic pumps. Given a NESS characterized by a particular set of stationary probabilities, currents, and entropy production rates, we show how to construct a SP with exactly the same (time-averaged) values. The mapping works in the opposite direction as well. These results establish a proof of principle: They show that stochastic pumps are able to mimic the behavior of nonequilibrium steadystates, and vice versa, within the theoretical framework of discrete-state stochastic thermodynamics. Nonequilibrium steadystates and stochastic pumps are often used to model, respectively, biomolecular motors driven by chemical reactions and artificial molecular machines steered by the variation of external, macroscopic parameters. Our results loosely suggest that anything a biomolecular machine can do, an artificial molecular machine can do equally well. We illustrate this principle by showing that kinetic proofreading, a NESS mechanism that explains the low error rates in biochemical reactions, can be effectively mimicked by a constrained periodic driving.

Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steadystates under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steadystate is generically described by a thermodynamic universality class.

Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.

We address the issue of extending thermodynamics to nonequilibrium steadystates. Using driven stochastic lattice gases, we ask whether consistent definitions of an effective chemical potential μ, and an effective temperature Te, are possible. μ and Te are determined via coexistence, i.e., zero flux of particles and energy between the driven system and a reservoir. In the lattice gas with nearest-neighbor exclusion, temperature is not relevant, and we find that the effective chemical potential, a function of density and drive strength, satisfies the zeroth law, and correctly predicts the densities of coexisting systems. In the Katz-Lebowitz-Spohn driven lattice gas both μ and Te need to be defined. We show analytically that in this case the zeroth law is violated for Metropolis exchange rates, and determine the size of the violations numerically. The zeroth law appears to be violated for generic exchange rates. Remarkably, the system-reservoir coupling proposed by Sasa and Tasaki [J. Stat. Phys. 125, 125 (2006), 10.1007/s10955-005-9021-7] is free of inconsistencies, and the zeroth law holds. This is because the rate depends only on the state of the donor system, and is independent of that of the acceptor.

Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics. PMID:26837464

Summary Background: the purpose of this study was to verify the validity of respiratory compensation threshold (RCT) measured during a new single judo specific incremental test (JSIT) for aerobic demand evaluation. Methods: to test the validity of the new test, the JSIT was compared with Maximal Lactate SteadyState (MLSS), which is the gold standard procedure for aerobic demand measuring. Eight well-trained male competitive judo players (24.3 ± 7.9 years; height of 169.3 ± 6.7cm; fat mass of 12.7 ± 3.9%) performed a maximal incremental specific test for judo to assess the RCT and performed on 30-minute MLSS test, where both tests were performed mimicking the UchiKomi drills. Results: the intensity at RCT measured on JSIT was not significantly different compared to MLSS (p=0.40). In addition, it was observed high and significant correlation between MLSS and RCT (r=0.90, p=0.002), as well as a high agreement. Conclusions: RCT measured during JSIT is a valid procedure to measure the aerobic demand, respecting the ecological validity of Judo. PMID:25332923

Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics. PMID:26837464

Mathematical modeling of genetic circuits generally assumes that gene expression is at steadystate when measurements are performed. However, conventional methods of measurement do not necessarily guarantee that this assumption is satisfied. In this study, we reveal a bi-plateau mode of gene expression at the single-cell level in bacterial batch cultures. The first plateau is dynamically active, where gene expression is at steadystate; the second plateau, however, is dynamically inactive. We further demonstrate that the predictability of assembled genetic circuits in the first plateau (steadystate) is much higher than that in the second plateau where conventional measurements are often performed. By taking the nature of steadystate into consideration, our method of measurement promises to directly capture the intrinsic property of biological parts/circuits regardless of circuit-host or circuit-environment interactions. PMID:26652307

We articulate an adaptive and reference-free framework based on the principle of random switching to detect and control unstable steadystates in high-dimensional nonlinear dynamical systems, without requiring any a priori information about the system or about the target steadystate. Starting from an arbitrary initial condition, a proper control signal finds the nearest unstable steadystate adaptively and drives the system to it in finite time, regardless of the type of the steadystate. We develop a mathematical analysis based on fast-slow manifold separation and Markov chain theory to validate the framework. Numerical demonstration of the control and detection principle using both classic chaotic systems and models of biological and physical significance is provided. PMID:26565299

Molecular dynamics (MD) simulations are used to investigate the steady-state shear flow curves of a standard glass model: the bidisperse Lennard-Jones system. For a wide range of temperatures in the neighborhood of the glass transition temperature Tg predicted by the mode coupling theory, we compute the steady-state shear stress and viscosity as a function of the shear rate γ ˙. At temperatures near and above Tg, the stress crosses over from linear Newtonian behavior at low rates to power law shear-thinning at high rates. As T decreases below Tg, the stress shows a plateau, becoming nearly rate-independent at low γ ˙. There is a weak increase in stress that is consistent with Eyring theory for activated flow of a solid. We find that when the strain rate is reduced to extremely low values, Newtonian behavior appears once more. Insights gained from these simulations are applied to the computation of flow curves of a well-established boundary lubricant: squalane. In the elastohydrodynamic regime, squalane responds like a glassy solid with an Eyring-like response, but at low rates it has a relatively small Newtonian viscosity. Supported by the Army Research Laboratory under Grant W911NF-12-2-0022.

Patients on HAART for long periods of time obtain viral loads (VLs) below 50 copies/ml. Ultrasensitive VL assays show that some of these patients obtain a low steadystate VL, while others continue to exhibit VL declines to below 5 copies/ml. Low steadystates can be explained by two-compartment models that incorporate a drug sanctuary. Interestingly, when patients exhibit continued declines below 50 copies/ml the rate of decline has a half-life of {approx} 6 months, consistent with some estimates of the rate of latent cell decline. Some patients, despite having sustained undetectable VLs show periods of transient viremia (blips). I will present some statistical characterization of the blips observed in a set of 123 patients, suggesting that blips are generated largely by random processes, that blips tend to correspond to periods of a few weeks in which VLs are elevated, and that VL decay from the peak of a blip may have two-phases. Using new results suggesting that the viral burst size, N {approx} 5 x 10{sup 4}, we estimate the number of cells needed to produce a blip.

Despite decades of scientific observation of rivers, streams and laboratory experiments the process of erosion still is not understood. Empirical fits are used to determine when erosion starts with more than an order of magnitude scatter or a shifting power law determining how much material erodes away. In order to study the many body problem of multiple particles we first need to understand the basics of a single particle eroding from a potential well in laminar flow. Using different particle densities and different barrier heights we looked at the onset of erosion and the balance of forces and torques to create a predictive model of when a single particle will erode over a barrier of a given height as a function of shear rate and viscosity. We then create a steadystate system in which to image erosion as it happens and simultaneously measure flow velocity and particle movement. Measuring particle movement allows us to determine when steadystate erosion occurs and calculate the fluxes and slip velocities at the beginning of the erosion process as we transition from rolling particles to particles suspended in the fluid flow. NSF Grant Number CBET 1335928.

The authors present a two-dimensional, force-balanced magnetic field model in which flux tubes have constant pV{gamma} throughout an extended region of the nightside plasma sheet, between approximately 36 R{sub E} geocentric distance and the region of the inner edge of the plasma sheet. They have thus demonstrated the theoretical existence of a steadystate magnetic field configuration that is force-balanced and also consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD (isotropic pressure, perfect conductivity). The numerical solution was constructed for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The primary characteristics of the steadystate convection solution are (1) a pressure maximum just tailward of the inner edge of the plasma sheet and (2) a deep, broad minimum in equatorial magnetic field strength B{sub ze}, also just tailward of the inner edge. The results are consistent with Erickson's (1985) convection time sequences, which exhibited analogous pressure peaks and B{sub ze} minima. Observations do not indicate the existence of a B{sub ze} minimum, on the average. They suggest that the configurations with such deep minima in B{sub ze} may be tearing-mode unstable, thus leading to substorm onset in the inner plasma sheet.

Groundwater recharge simulation under the steady-state and transient climate conditions Diffusive groundwater recharge is a vertical water flux through the water table, i.e. through the boundary between the unsaturated and saturated zones. This flux features temporal and spatial changes due to variations in the climatic conditions, landscape the state of vegetation, and the spatial variability of vadoze zone characteristics. In a changing climate the non-steadystate series of climatic characteristics will affect on the groundwater recharge.. A well-tested approach to calculating water flux through the vadoze zone is the application of Richard’s equations for a heterogeneous one-domain porosity continuum with specially formulated atmospheric boundary conditions at the ground surface. In this approach the climatic parameters are reflected in upper boundary conditions, while the recharge series is the flux through the low boundary. In this work developed by authors code Surfbal that simulates water cycle at surface of topsoil to take into account the various condition of precipitation transformation at the surface in different seasons under different vegetation cover including snow accumulation in winter and melting in spring is used to generate upper boundary condition at surface of topsoil for world-wide known Hydrus-1D code (Simunek et al, 2008). To estimate the proposal climate change effect we performed Surfbal and Hydrus simulation using the steadystate climatic condition and transient condition due to global warming on example of Moscow region, Russia. The following scenario of climate change in 21 century in Moscow region was selected: the annual temperature will increase on 4C during 100 year and annual precipitation will increase on 10% (Solomon et al, 2007). Within the year the maximum increasing of temperature and precipitation falls on winter time, while in middle of summer temperature will remain almost the same as observed now and monthly

Three experiments were conducted to define steady -state features of timbre for a group of well-trained musicians. Experiment 1 evaluated whether or not pairs of three critical dimensions of timbre--spectral slope (6 or 12 dB/octave), formant structure (/a/ or /i/ vowel), and inharmonicity of partials (harmonic or inharmonic)--were processed in a separable or integral fashion. Accuracy and speed for classification of values along one dimension were examined under different conditions of variability along a second dimension (fixed, correlated, or orthogonal). Spectral slope and formant structure were integral, with classification speed for the target dimension depending upon variability along the orthogonal dimension. In contrast, evidence of asymmetric separability was obtained for inharmonicity. Classification speed for slope and formant structure did not depend on inharmonicity, whereas RT for the target dimension of inharmonicity was strongly influenced by variability along either slope or formant structure. Since the results of Experiment 1 provided a basis for manipulating spectral slope and formant structure as a single feature, these dimensions were correlated in Experiment 2. Subjects searched for targets containing potential features of timbre within arrays of 1-4 inharmonic distractor pitches. Distractors were homogeneous with respect to the dimensions of timbre. When targets had /a/ formants with shallow spectral slopes, search time increased nonlinearly with array size in a manner consistent with the parallel processing of items, and thus feature search. Feature search was not obtained for targets with /i/ formants and steep slopes. Thus, the feature was coded as the presence or absence of /a/ formants with shallow spectral slopes. A search task using heterogeneous distractor values along slope/formant structure was used in Experiment 3 to evaluate whether or not the feature of timbre and pitch were automatically conjoined (integral). Search times for

Boolean networks have been widely used to model biological processes lacking detailed kinetic information. Despite their simplicity, Boolean network dynamics can still capture some important features of biological systems such as stable cell phenotypes represented by steadystates. For small models, steadystates can be determined through exhaustive enumeration of all state transitions. As the number of nodes increases, however, the state space grows exponentially thus making it difficult to find steadystates. Over the last several decades, many studies have addressed how to handle such a state space explosion. Recently, increasing attention has been paid to a satisfiability solving algorithm due to its potential scalability to handle large networks. Meanwhile, there still lies a problem in the case of large models with high maximum node connectivity where the satisfiability solving algorithm is known to be computationally intractable. To address the problem, this paper presents a new partitioning-based method that breaks down a given network into smaller subnetworks. Steadystates of each subnetworks are identified by independently applying the satisfiability solving algorithm. Then, they are combined to construct the steadystates of the overall network. To efficiently apply the satisfiability solving algorithm to each subnetwork, it is crucial to find the best partition of the network. In this paper, we propose a method that divides each subnetwork to be smallest in size and lowest in maximum node connectivity. This minimizes the total cost of finding all steadystates in entire subnetworks. The proposed algorithm is compared with others for steadystates identification through a number of simulations on both published small models and randomly generated large models with differing maximum node connectivities. The simulation results show that our method can scale up to several hundreds of nodes even for Boolean networks with high maximum node connectivity. The

Our purpose is to construct a theoretical description of non-equilibrium steadystate (NESS), employing thermo field dynamics (TFD). TFD is the operator-based formalism of thermal quautum field theory, where every degree of freedom is doubled and thermal averages are given by expectation values of the thermal vacuum. To specify the thermal vacuum for NESS is a non-trivial issue, and we attempt it on the analogy between the superoperator formalism and TFD. Using the thermal vacuum thus obtained, we analyze the NESS which is realized in the two-reservoir model. It will be shown that the NESS vacuum of the model coincides with the fixed point solutions of the quantum transport equation derived by the self-consistent renormalization of the self-energy in non-equilibrium TFD.

An analytic solution is presented for the steadystate electric and magnetic fields induced by the motional electric field of the solar wind in the atmosphere or interior of a planet that is asymmetrically surrounded by solar wind plasma. The electrically conducting ionosphere or interior must be in direct electrical contact with the solar wind over the day side of the planet. The conducting region of the planet is modeled by a sphere or a spherical shell of arbitrarily stratified electrical conductivity. A monoconducting cylindrical cavity is assumed to extend downstream on the night side of the planet. The solar wind is assumed to be highly conducting so that the induced fields are confined to the planet and cavity. Induced currents close as sheet currents at the solar wind-cavity and solar wind-planet interfaces. Numerical evaluations of the analytic formulas are carried out for a uniformly conducting spherical model.

We have applied a self-consistent 1-Dmodel for heat diffusion, vapor diffusion, and ice condensation/sublimation, and surface energy balance to investigate our hypothesis for the source of the recently observed water vapor around Ceres [1]. As described in a companion presentation [2], we find that the estimated global flux of 6 kg/s can be produced by steady-state sublimation of subsurface ice driven by the “geothermal” temperature gradient for a heat flux of 1 mW/m2 - the value estimated for a chondritic abundance of heat-producing elements [3,4]. We will present a detailed description of our Ceres cryothermal diffusion model and comparisons with previous models. One key difference is the use of a new physics-based analytic model (‘MaxRTCM’) for calculating the thermal conductivity (Kth) of planetary regolith [5] that has been validated by comparisons to a wide range of laboratory data [6]. MaxRTCM predicts much lower Kth values in the upper regolith than those in previous work [3]. It also accounts for a process first modeled in a study of unstable equatorial ground ice on Mars [7,8], where vapor diffusing up from a receding ice table toward the surface can recondense at shallower depths - eventually forming a steady-state profile of pore ice volume fraction that increases with depth and maintains a constant flux of vapor at all depths [7]. Using MaxRTCM we calculate the corresponding Kth(z) profiles and will present predictions and implications of the resulting temperature profile in the upper few kilometers of Ceres’ megaregolith.References: [1] Küppers et al. (2014), Nature, 505(7484), 525-527. [2] Wood et al., 2014, this meeting. [3] Fanale & Salvail (1989) Icarus 82, 97-110. [4] McCord and Sotin (2005) JGR 110, E05009. [5] Wood (2013) LPSC Abs. 44, 3077. [6] Wood (2014), Icarus, in revision. [7] Mellon et al. (1997), JGR, 102, 19357-69. [8] Clifford (1993), JGR, 98, 10973-11016.

A pharmacokinetic model was constructed to explain the difference in brain- and cerebrospinal fluid (CSF)-to-plasma and brain-to-CSF unbound drug concentration ratios (Kp,uu,brain, Kp,uu,CSF, and Kp,uu,CSF/brain, respectively) of drugs under steady-state conditions in rats. The passive permeability across the blood-brain barrier (BBB), PS1, was predicted by two methods using log(D/molecular weight(0.5)) for PS1(1) or the partition coefficient in octanol/water at pH 7.4 (LogD), topologic van der Waals polar surface area, and van der Waals surface area of the basic atoms for PS1(2). The coefficients of each parameter were determined using previously reported in situ rat BBB permeability. Active transport of drugs by P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) measured in P-gp- and Bcrp-overexpressing cells was extrapolated to in vivo by introducing scaling factors. Brain- and CSF-to-plasma unbound concentration ratios (Kp,uu,brain and Kp,uu,CSF, respectively) of 19 compounds, including P-gp and Bcrp substrates (daidzein, dantrolene, flavopiridol, genistein, loperamide, quinidine, and verapamil), were simultaneously fitted to the equations in a three-compartment model comprising blood, brain, and CSF compartments. The calculated Kp,uu,brain and Kp,uu,CSF of 17 compounds were within a factor of three of experimental values. Kp,uu,CSF values of genistein and loperamide were outliers of the prediction, and Kp,uu,brain of dantrolene also became an outlier when PS1(2) was used. Kp,uu,CSF/brain of the 19 compounds was within a factor of three of experimental values. In conclusion, the Kp,uu,CSF/brain of drugs, including P-gp and Bcrp substrates, could be successfully explained by a kinetic model using scaling factors combined with in vitro evaluation of P-gp and Bcrp activities. PMID:24644297

Metabolic networks are often extremely complex. Despite intensive efforts many details of these networks, e.g., exact kinetic rates and parameters of metabolic reactions, are not known, making it difficult to derive their properties. Considerable effort has been made to develop theory about properties of steadystates in metabolic networks that are valid for any values of parameters. General results on uniqueness of steadystates and their stability have been derived with specific assumptions on reaction kinetics, stoichiometry and network topology. For example, deep results have been obtained under the assumptions of mass-action reaction kinetics, continuous flow stirred tank reactors (CFSTR), concordant reaction networks and others. Nevertheless, a general theory about properties of steadystates in metabolic networks is still missing. Here we make a step further in the quest for such a theory. Specifically, we study properties of steadystates in metabolic networks with monotonic kinetics in relation to their stoichiometry (simple and general) and the number of metabolites participating in every reaction (single or many). Our approach is based on the investigation of properties of the Jacobian matrix. We show that stoichiometry, network topology, and the number of metabolites that participate in every reaction have a large influence on the number of steadystates and their stability in metabolic networks. Specifically, metabolic networks with single-substrate-single-product reactions have disconnected steadystates, whereas in metabolic networks with multiple-substrates-multiple-product reactions manifolds of steadystates arise. Metabolic networks with simple stoichiometry have either a unique globally asymptotically stable steadystate or asymptotically stable manifolds of steadystates. In metabolic networks with general stoichiometry the steadystates are not always stable and we provide conditions for their stability. In order to demonstrate the biological

In the framework of density functional theory, a formalism to describe electronic transport in the steadystate is proposed which uses the density on the junction and the steady current as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential, and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds. At small currents these steps emerge as the equilibrium xc discontinuity bifurcates. The formalism is applied to a model benzene junction, finding perfect agreement with the orthodox theory of Coulomb blockade. PMID:26571349

NASA Glenn Research Center (GRC) has developed the LERCHP code. The PC-based LERCHP code can be used to predict the steady-state performance of heat pipes, including the determination of operating temperature and operating limits which might be encountered under specified conditions. The code contains a vapor flow algorithm which incorporates vapor compressibility and axially varying heat input. For the liquid flow in the wick, Darcy s formula is employed. Thermal boundary conditions and geometric structures can be defined through an interactive input interface. A variety of fluid and material options as well as user defined options can be chosen for the working fluid, wick, and pipe materials. This report documents the current effort at GRC to update the LERCHP code for operating in a Microsoft Windows (Microsoft Corporation) environment. A detailed analysis of the model is presented. The programming architecture for the numerical calculations is explained and flowcharts of the key subroutines are given

We perform a quasi-steady-state (QSS) reduction of a flashing ratchet to obtain a Brownian particle in an effective potential. The resulting system is analytically tractable and yet preserves essential dynamical features of the full model. We first use the QSS reduction to derive an explicit expression for the velocity of a simple two-state flashing ratchet. In particular, we determine the relationship between perturbations from detailed balance, which are encoded in the transitions rates of the flashing ratchet, and a tilted-periodic potential. We then perform a QSS analysis of a pair of elastically coupled flashing ratchets, which reduces to a Brownian particle moving in a two-dimensional vector field. We suggest that the fixed points of this vector field accurately approximate the metastable spatial locations of the coupled ratchets, which are, in general, impossible to identify from the full system.

In recent years, compositional modeling and self-explanatory simulation techniques have simplified the process of building dynamic simulators of physical systems. Building steady-state simulators is, conceptually, a simpler task consisting in solving a set algebraic equations. This simplicity hides delicate technical issues of convergence and search-space size due to the potentially large number of unknown parameters. We present an automated technique for reducing the dimensionality of the problem by (1) automatically identifying feedback loops (a generally NP-complete problem), (2) hierarchically decomposing the set of equations in terms of feedback loops, and (3) structuring a simulator where equations are solved either serially without search or in isolation within a feedback loop. This paper describes the key algorithms and the results of their implementation on building simulators for a two-phase evaporator loop system across multiple combinations of causal and non-causal approximations.

Dynamic evolution of initial instability is investigated by an analytic model obtained by modifying the theory of Warren and Langer [Phys. Rev. E 47, 2702 (1993)] and the quantitative phase-field model in directional solidification under transient conditions for realistic parameters of a dilute alloy. The evolutions of tip velocity and concentration in the liquid side of the interface predicted by the analytic model agree very well with that from the phase-field simulation in the linear growth stage of the non-steady-state growth, indicating that the model could be used as a convenient method to study the initial instability during non-steady-state growth. The influences of non-steady-state conditions which include the increasing rate of pulling speed and temperature gradient at the onset of initial instability are investigated, and we find that, the initial instability seems to depend strongly on the non-steady-state conditions and the non-steady-state history, and thus, it should be primarily considered in the study of the transient growth. PMID:25019790

Dynamic evolution of initial instability is investigated by an analytic model obtained by modifying the theory of Warren and Langer [Phys. Rev. E 47, 2702 (1993), 10.1103/PhysRevE.47.2702] and the quantitative phase-field model in directional solidification under transient conditions for realistic parameters of a dilute alloy. The evolutions of tip velocity and concentration in the liquid side of the interface predicted by the analytic model agree very well with that from the phase-field simulation in the linear growth stage of the non-steady-state growth, indicating that the model could be used as a convenient method to study the initial instability during non-steady-state growth. The influences of non-steady-state conditions which include the increasing rate of pulling speed and temperature gradient at the onset of initial instability are investigated, and we find that, the initial instability seems to depend strongly on the non-steady-state conditions and the non-steady-state history, and thus, it should be primarily considered in the study of the transient growth.

The accuracy of non-steady-state equations for measuring changes in free fatty acid rate of appearance (Ra) is unknown. In the present study, endogenous lipolysis (traced with ({sup 14}C)-linoleate) was pharmacologically suppressed in six conscious mongrel dogs. A computer-responsive infusion pump was then used to deliver an intravenous oleic acid emulsion in both constant and linear gradient infusion modes. Both non-steady-state equations with various effective volumes of distribution (V) and steady-state equations were used to measure oleate Ra (({sup 14}C)oleate). Endogenous lipolysis did not change during the experiment. When oleate Ra increased in a linear gradient fashion, only non-steady-state equations with a large (150 ml/kg) V resulted in erroneous values (9% overestimate, P less than 0.05). In contrast, when oleate Ra decreased in a similar fashion, steady-state and standard non-steady-state equations (V = plasma volume = 50 ml/kg) overestimated total oleate Ra (18 and 7%, P less than 0.001 and P less than 0.05, respectively). Overall, non-steady-state equations with an effective V of 90 ml/kg (1.8 x plasma volume) allowed the most accurate estimates of oleate Ra.

A 1Dsteady-statemodel is developed to deal with stimulated scattering processes. The volume and boundary noise sources for scattered light are discussed in detail. Our results indicate that the boundary noise sources may play a significant role in estimating the reflectivity of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). With the capability of our model to deal with broadband scattered light, we find that pump depletion could be the main reason to the anti-correlation between SBS and SRS versus electron density observed in experiments. A simple method is proposed to phenomenologically include the effect of nonlinear saturation mechanisms in our model and reasonable results are obtained.

Penning-Malmberg traps provide an excellent method to confine single-component plasmas. Specially tailored, high-density plasmas can be created in these devices by the application of azimuthally phased rf fields [i.e., the so-called ``rotating wall'' (RW) technique]. Recently, we reported a new regime of RW compression of electron (or positron) plasmas ootnotetextJ. R. Danielson and C. M. Surko, Phys. Rev. Lett. 95, 035001 (2005).. In this ``strong-drive'' regime, plasmas are compressed until the E x B rotation frequency, φE (with φE plasma density) approaches the applied frequency, φRW. Good compression is achieved over a broad range of RW frequencies, without the need to tune to a mode in the plasma. The resulting steady-state density is found to be only weakly dependent on the applied RW amplitude. A simple nonlinear dynamical model explains these observations as convergence to an attracting fixed point - the torque-balanced steadystate. The applied RW torque, τRW, can be understood as a generic, linear coupling between the plasma and the Debye- shielded RW electric field. The thermodynamic equations ootnotetextT. M. O'Neil and D. H. E. Dubin, Phys. Plasmas 5, 2163 (1998). governing the evolution will be discussed and compared to the experiments. This new regime facilitates improved compression and colder plasmas (since less transport means less plasma heating). Factors limiting the utility of the technique and applications will be discussed, including the development of a multicell trap to confine large numbers (i.e., N >=10^ 12) of positrons ootnotetextC. M. Surko and R. G. Greaves, Phys. Plasmas 11, 2333 (2004)..

A general approach is presented for analyzing the steady-state creep response and its underlying mechanisms in metal-ceramic multilayers subjected to monotonic or cyclic variations in temperature. This approach combines the plate or beam theories of continuum mechanics with the mechanism-based classical constitutive equations for steady-state creep. The method is capable of predicting the evolution of overall curvature in the layered solid, the generation of thermal stresses within each layer, and the dominant deformation mechanisms at any through-thickness location of each layer at any instant of time or temperature for prescribed layer geometries, thermo-mechanical properties of the constituent layers, and the applied thermal history. Simulations are presented for Al-Al{sub 2}O{sub 3} bilayer and Al{sub 2}O{sub 3}-Al-Al{sub 2}O{sub 3} trilayer model systems. The predicted results are compared with appropriate experimental measurements for the bilayers subjected to thermal cycling up to 450 C. It is found that the multilayer creep calculations capture the essential features of cyclic thermal response; the extent of stress relaxation in the Al layer, however, is somewhat overestimated, especially at higher temperatures. Possible reasons for such discrepancy are discussed, and the significance and limitations of the overall approach are highlighted. The effects of the rate of heating or cooling on deformation, and the correlations between the present creep analyses and rate-independent elastoplastic formulations for multilayers are also considered. The influence of layer thickness on the evolution of creep mechanisms is also examined from thick multilayers to the limiting case of a thin metallic film on a brittle substrate.

We discuss a simple quantum thermal machine for the generation of steady-state entanglement between two interacting qubits. The machine is autonomous in the sense that it uses only incoherent interactions with thermal baths, but no source of coherence or external control. By weakly coupling the qubits to thermal baths at different temperatures, inducing a heat current through the system, steady-state entanglement is generated far from thermal equilibrium. Finally, we discuss two possible implementations, using superconducting flux qubits or a semiconductor double quantum dot. Experimental prospects for steady-state entanglement are promising in both systems.

A constructive criterion for decoupling the steadystates of a linear time-invariant multivariable system is presented. This criterion consists of a set of inequalities which, when satisfied, will cause the steadystates of a system to be decoupled. Stability analysis and a new design technique for such systems are given. A new and simple connection between single-loop and multivariable cases is found. These results are then applied to the compensation design for NASA STOL C-8A aircraft. Both steady-state decoupling and stability are justified through computer simulations.

Based on the optimality principle (that the global energy expenditure rate is at its minimum for a given landscape under steadystate conditions) and calculus of variations, we have derived a group of partial differential equations for describing steady-state optimal landscapes without explicitly distinguishing between hillslopes and channel networks. Other than building on the well-established Mining's equation, this work does not rely on any empirical relationships (such as those relating hydraulic parameters to local slopes). Using additional constraints, we also theoretically demonstrate that steady-state water depth is a power function of local slope, which is consistent with field data.

This paper presents the electromagnetic analysis of a high voltage saturated-core superconducting fault current limiter (SCSFCL). The numerical analyses of a three-dimensional (3D) model is shown, and the specific parameters are given. The model focus on the steady-state impedance of the limiter when connected to the power grid. It analyzed the dependence of steady-state impedance on the AC coil current, and the relationship between oil gap and coil inductance. The results suggest that, adding oil gap between slice of silicon steel can reduce the core cross-section, restrain the ultraharmonic and decrease the steady-state impedance. As the core cross-section of AC limb decreased from 4344 cm2 to 3983 cm2, the total harmonic distortion for voltage decreased from 2.4% to 1.8%, and the impedance decreased from 1.082 Ω to 1.069 Ω(Idc=400A,Iac=1296A).

The definition of potential evaporation remains widely debated despite its centrality for hydrologic and climatic models. We employed an analytical pore-scale representation of evaporation from porous surfaces to define potential evaporation using a hypothetical steady-state reference temperature for air and evaporating surface. The feedback between drying land surfaces and overlaying air properties is implicitly incorporated in the hypothetical steady-state where the sensible heat flux vanishes and available energy is consumed by evaporation. Potential evaporation based on steady-state surface temperature was in surprisingly good agreement with class A pan evaporation measurements suggesting that pan evaporation occurs with negligible sensible heat flux. The model facilitates a new analytical generalization of the asymmetric complementary relationship across a wide range of meteorological conditions with good agreement between measured and predicted actual evaporation.

We show that the steadystates of the classical Heisenberg XXX spin-chain in an external magnetic field can be found by iterations of a quaternionic map. A restricted model, e.g., the xy spin-chain is known to have spatially chaotic steadystates and the phase space occupied by these chaotic states is known to go through discrete changes as the field strength is varied. The same phenomenon is studied for the xxx spin-chain. It is seen that in this model the phase space volume varies smoothly with the external field.

Spatially resolved steady-state photocarrier radiometric (PCR) imaging technique is developed to characterize the electronic transport properties of silicon wafers. Based on a nonlinear PCR theory, simulations are performed to investigate the effects of electronic transport parameters (the carrier lifetime, the carrier diffusion coefficient, and the front surface recombination velocity) on the steady-state PCR intensity profiles. The electronic transport parameters of an n-type silicon wafer are simultaneously determined by fitting the measured steady-state PCR intensity profiles to the three-dimensional nonlinear PCR model. The determined transport parameters are in good agreement with the results obtained by the conventional modulated PCR technique with multiple pump beam radii.

This unit describes the experimental procedures for the steady-state kinetic analysis of DNA synthesis across DNA nucleotides (native or modified) by DNA polymerases. In vitro primer extension experiments with a single nucleoside triphosphate species followed by denaturing polyacrylamide gel electrophoresis of the extended products is described. Data analysis procedures and fitting to steady-state kinetic models is presented to highlight the kinetic differences involved in the bypass of damaged versus undamaged DNA. Moreover, explanations concerning problems encountered in these experiments are addressed. This approach provides useful quantitative parameters for the processing of damaged DNA by DNA polymerases. PMID:25501593

Longitudinal profiles of natural streams are known to show concave forms. Saying A as drainage area, channel gradient S can be expressed as the power-law, S≈A-θ (Flint, 1974), which is one of the scale-invariant features of drainage basin. According to literature, θ of most natural streams falls into a narrow range (0.4 < θ < 0.7) (Tucker and Whipple, 2002). It leads to fundamental questions: 'Why does θ falls into such narrow range?' and 'How is this related with other power-law scaling relationships reported in natural drainage basins?' To answer above questions, we analytically derive θ for a steady-state drainage basin following Lane's equilibrium (Lane, 1955) throughout the corridor and named this specific case as the 'critical concavity'. In the derivation, sediment transport capacity is estimated by unit stream power model (Yang, 1976), yielding a power function of upstream area. Stability of channel at a local point occurs when incoming flux equals outgoing flux at the point. Therefore, given the drainage at steady-state where all channel beds are stable, the exponent of the power function should be zero. From this, we can determine the critical concavity. Considering ranges of variables associated in this derivation, critical concavity cannot be resolved as a single definite value, rather a range of critical concavity is suggested. This range well agrees with the widely reported range of θ (0.4 < θ < 0.7) in natural streams. In this theoretical study, inter-relationships between power-laws such as hydraulic geometry (Leopold and Maddock, 1953), dominant discharge-drainage area (Knighton et al., 1999), and concavity, are coupled into the power-law framework of stream power sediment transport model. This allows us to explore close relationships between their power-law exponents: their relative roles and sensitivity. Detailed analysis and implications will be presented. References Flint, J. J., 1974, Stream gradient as a function of order, magnitude

In this paper the authors describe progress on validating a number of local transport models by comparing their predictions with relevant experimental data from a range of tokamaks in the ITER profile database. This database, the testing procedure and results are discussed. In addition a model for sawtooth oscillations is used to investigate their effect in an ITER plasma with alpha-particles.

We use three different statistical models describing the frequency of meteoroid impacts on Earth to estimate the seismic background noise due to impacts on the lunar surface. Because of diffraction, seismic events on the Moon are typically characterized by long codas, lasting 1 h or more. We find that the small but frequent impacts generate seismic signals whose codas overlap in time, resulting in a permanent seismic noise that we term the "lunar hum" by analogy with the Earth's continuous seismic background seismic hum. We find that the Apollo era impact detection rates and amplitudes are well explained by a model that parameterizes (1) the net seismic impulse due to the impactor and resulting ejecta and (2) the effects of diffraction and attenuation. The formulation permits the calculation of a composite waveform at any point on the Moon due to simulated impacts at any epicentral distance. The root-mean-square amplitude of this waveform yields a background noise level that is about 100 times lower than the resolution of the Apollo long-period seismometers. At 2 s periods, this noise level is more than 1000 times lower than the low noise model prediction for Earth's microseismic noise. Sufficiently sensitive seismometers will allow the future detection of several impacts per day at body wave frequencies. Copyright 2009 by the American Geophysical Union.

The equations describing the distributions and concentrations of trace species are nonlinear and may thus possess more than one solution. This paper develops methods for searching for multiple physical solutions to chemical continuity equations and applies these to subsets of equations describing tropospheric chemistry. The calculations are carried out with a box model and use two basic strategies. The first strategy is a 'search' method. This involves fixing model parameters at specified values, choosing a wide range of initial guesses at a solution, and using a Newton-Raphson technique to determine if different initial points converge to different solutions. The second strategy involves a set of techniques known as homotopy methods. These do not require an initial guess, are globally convergent, and are guaranteed, in principle, to find all solutions of the continuity equations. The first method is efficient but essentially 'hit or miss' in the sense that it cannot guarantee that all solutions which may exist will be found. The second method is computationally burdensome but can, in principle, determine all the solutions of a photochemical system. Multiple solutions have been found for models that contain a basic complement of photochemical reactions involving O(x), HO(x), NO(x), and CH4. In the present calculations, transitions occur between stable branches of a multiple solution set as a control parameter is varied. These transitions are manifestations of hysteresis phenomena in the photochemical system and may be triggered by increasing the NO flux or decreasing the CH4 flux from current mean tropospheric levels.

Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeasts have proteins, which can undergo similar reconformation and aggregation processes to PrP; yeast ``prions" are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein (1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics along with our own stochastic approach (2). Both models assume reconformation only upon aggregation, and include aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates.

Kinetics of steady-state copolymerization has been investigated since the 1940s. Irreversible terminal and penultimate models were successfully applied to a number of comonomer systems, but failed for systems where depropagation is significant. Although a general mathematical treatment of the terminal model with depropagation was established in the 1980s, a penultimate model and higher-order terminal models with depropagation have not been systematically studied, since depropagation leads to hierarchically-coupled and unclosed kinetic equations which are hard to solve analytically. In this work, we propose a truncation method to solve the steady-state kinetic equations of any-order terminal models with depropagation in a unified way, by reducing them into closed steady-state equations which give the exact solution of the original kinetic equations. Based on the steady-state equations, we also derive a general thermodynamic equality in which the Shannon entropy of the copolymer sequence is explicitly introduced as part of the free energy dissipation of the whole copolymerization system. PMID:25992648

In recent years, inkjet technology has played an important role in industrial materials printing and various sensors fabrication, but the mechanisms of the inkjet print head should be researched more elaborately. The steadystate deformation analysis of a tubular piezoelectric print head, which can be classified as a plane strain problem because the radii of the tubes are considerably smaller than the lengths, is discussed in this paper. The geometric structure and the boundary conditions are all axisymmetric, so a one-dimensional mathematical model is constructed. By solving the model, the deformation field and stress field, as well as the electric potential distribution of the piezoelectric tube and glass tube, are obtained. The results show that the deformations are on the nanometer scale, the hoop stress is larger than the radial stress on the whole, and the potential is not linearly distributed along the radial direction. An experiment is designed to validate these computations. A discussion of the effect of the tubes' thicknesses on the system deformation status is provided. PMID:26771612

Seasonal studies of the vertical distribution of nitrate, nitrite, and phytoplankton in the oceans and studies using /sup 15/N as a tracer of nitrate metabolism indicate that the reduction of nitrate by phytoplankton is a source of nitrite in the upper waters of the ocean. To better understand this process, the relationship between nitrate uptake and nitrite production has been examined with continuous cultures of the small marine diatom Thalassiosira pseudonana. In a turbidostat culture, the rates of nitrite production by T. Pseudonana increase with light intensity. This process is only loosely coupled to rates of nitrate assimilation since the ratio of net nitrite production to total nitrate assimilation increases with increased rates of growth. In continuous cultures where steady-state concentrations of nitrate and nitrite were varied, T. pseudonana produced nitrite at rates which increased with increasing concentrations of nitrate. Again, the rates of nitrite production were uncoupled from rates of nitrate assimilation. The study was used to derive a mathematical description of nitrate and nitrite metabolism by T. pseudonana. The validity of this model was supported by the results of a study in which /sup 15/N-labeled nitrite was introduced into the continuous culture, and the model was used to examine patterns in distribution of nitrite in the Antarctic Ocean and the Sargasso Sea.

In recent years, inkjet technology has played an important role in industrial materials printing and various sensors fabrication, but the mechanisms of the inkjet print head should be researched more elaborately. The steadystate deformation analysis of a tubular piezoelectric print head, which can be classified as a plane strain problem because the radii of the tubes are considerably smaller than the lengths, is discussed in this paper. The geometric structure and the boundary conditions are all axisymmetric, so a one-dimensional mathematical model is constructed. By solving the model, the deformation field and stress field, as well as the electric potential distribution of the piezoelectric tube and glass tube, are obtained. The results show that the deformations are on the nanometer scale, the hoop stress is larger than the radial stress on the whole, and the potential is not linearly distributed along the radial direction. An experiment is designed to validate these computations. A discussion of the effect of the tubes’ thicknesses on the system deformation status is provided. PMID:26771612

Mammalian prion proteins (PrP) are of public health interest because of mad cow and chronic wasting diseases. Yeast have proteins which can undergo similar reconformation and aggregation processes to PrP; yeast forms are simpler to experimentally study and model. Recent in vitro studies of the SUP35 protein(1), showed long aggregates and pure exponential growth of the misfolded form. To explain this data, we have extended a previous model of aggregation kinetics(2). The model assumes reconformation only upon aggregation, and includes aggregate fissioning and an initial nucleation barrier. We find for sufficiently small nucleation rates or seeding by small dimer concentrations that we can achieve the requisite exponential growth and long aggregates. We will compare to a more realistic stochastic kinetics model and present prelimary attempts to describe recent experiments on SUP35 strains. *-Supported by U.S. Army Congressionally Mandated Research Fund. 1) P. Chien and J.S. Weissman, Nature 410, 223 (2001); http://online.kitp.ucsb.edu/online/bionet03/collins/. 2) J. Masel, V.A.> Jansen, M.A. Nowak, Biophys. Chem. 77, 139 (1999).

At a time of growing concern over the ethics of animal experimentation, mouse models are still an indispensable source of insight into the cardiovascular system and its most frequent pathologies. Nevertheless, reference data on the murine cardiovascular anatomy and physiology are lacking. In this work, we developed and validated an in silico, one dimensional model of the murine systemic arterial tree consisting of 85 arterial segments. Detailed aortic dimensions were obtained in vivo from contrast-enhanced micro-computed tomography in 3 male, C57BL/6J anesthetized mice and 3 male ApoE(-/-) mice, all 12-weeks old. Physiological input data were gathered from a wide range of literature data. The integrated form of the Navier-Stokes equations was solved numerically to yield pressures and flows throughout the arterial network. The resulting model predictions have been validated against invasive pressure waveforms and non-invasive velocity and diameter waveforms that were measured in vivo on an independent set of 47 mice. In conclusion, we present a validated one-dimensional model of the anesthetized murine cardiovascular system that can serve as a versatile tool in the field of preclinical cardiovascular research. PMID:26555250

Computer program evaluates heat transfer modes and calculates either the transient or steady-state temperature distributions throughout an object of complex shape when heat sources are applied to specified points on the object. It uses an electrothermal model to simulate the conductance, heat capacity, and temperature potential of the object.

The historical pattern of resource allocation in American higher education as exemplified by public colleges in Colorado was examined. The reliance upon average cost information in making resource allocation decisions was critiqued for the special problems that arise from student enrollment decline or steadystate. A model of resource allocation…

Assess the steady-state flammability level at normal and off-normal ventilation conditions. The hydrogen generation rate was calculated for 177 tanks using the rate equation model. Flammability calculations based on hydrogen, ammonia, and methane were performed for 177 tanks for various scenarios.

Assess the steady-state flammability level at normal and off-normal ventilation conditions. The hydrogen generation rate was calculated for 177 tanks using the rate equation model. Flammability calculations based on hydrogen, ammonia, and methane were performed for 177 tanks for various scenarios.

In this paper, we consider a dynamical model of population biology which is of the classical Fisher type, but the competition interaction between individuals is nonlocal. The existence, uniqueness, and stability of the steadystate solution of the nonlocal problem on a bounded interval with homogeneous Dirichlet boundary conditions are studied.

This work is to assess the steady-state flammability level at normal and off-normal ventilation conditions in the tank dome space for 177 double-shell and single-shell tanks at Hanford. Hydrogen generation rate was calculated for 177 tanks using rate equation model developed recently.

The steady-state fluorescence anisotropy is employed to study the binding of protein of a model protein, human serum albumin, to a commonly used flavonoid, quercetin. The experiment describes the thermodynamics, as well as the biochemical interactions of such binding effectively.

... 40 Protection of Environment 2 2011-07-01 2011-07-01 false Steady-State Short Test Standards C... Short Test Standards (I) Short Test Standards for 1981 and Later Model Year Light-Duty Vehicles For 1981... altitude to which high altitude certification standards of 1.5 gpm HC and 15 gpm CO or less apply),...

We investigate nonequilibrium steadystates of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.

We report on a series of experiments in which a Hele-Shaw cell containing aqueous solutions of NH4Cl was translated at prescribed rates through a steady temperature gradient. The salt formed the primary solid phase of a mushy layer as the solution solidified, with the salt-depleted residual fluid driving buoyancy-driven convection and the development of chimneys in the mushy layer. Depending on the operating conditions, several morphological transitions occurred. A regime diagram is presented quantifying these transitions as a function of freezing rate and the initial concentration of the solution. In general, for a given concentration, increasing the freezing rate caused the steady-state system to change from a convecting mushy layer with chimneys to a non-convecting mushy layer below a relatively quiescent liquid, and then to a much thinner mushy layer separated from the liquid by a region of active secondary nucleation. At higher initial concentrations the second of these states did not occur. At lower concentrations, but still above the eutectic, the mushy layer disappeared. A simple mathematical model of the system is developed which compares well with the experimental measurements of the intermediate, non-convecting state and serves as a benchmark against which to understand some of the effects of convection. Movies are available with the online version of the paper.

The NASA Lewis heat pipe code was developed to predict the performance of heat pipes in the steadystate. The code can be used as a design tool on a personal computer or with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user.

ABSTRACT During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steadystate aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities. PMID:27412267

We investigate nonequilibrium steadystates of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state. PMID:26764644

The NASA Lewis heat pipe code has been developed to predict the performance of heat pipes in the steadystate. The code can be used as a design tool on a personal computer or, with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which the monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user.

A recent numerical approach for solving the advection-diffusion and Navier-Stokes equations is extended for the first time to a magnetohydrodynamic (MHD) model, aiming in particular consistent improvements over classical methods for investigating the magnetic reconnection process. In this study, we mainly focus on a two-dimensional incompressible set of resistive MHD equations written in flux-vorticity scalar variables. The originality of the method is based on hyperbolic reformulation of the dissipative terms, leading to the construction of an equivalent hyperbolic first-order (spatial derivatives) system. This enables the use of approximate Riemann solvers for handling dissipative and advective flux in the same way. A simple second-order finite-volume discretization on rectangular grids using an upwind flux is employed. The advantages of this method are illustrated by a comparison to two particular analytical steadystate solutions of the inviscid magnetic reconnection mechanism, namely the magnetic annihilation and the reconnective diffusion problems. In particular, the numerical solution is obtained with the same order of accuracy for the solution and gradient for a wide range of magnetic Reynolds numbers, without any deterioration characteristic of more conventional schemes. The amelioration of the hyperbolic method and its extension to time-dependent MHD problems related to solar flares mechanisms is also discussed.

During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steadystate aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities. PMID:27412267

A direct steady-state initialization (DSSI) method has been developed and implemented in the RELAP5 hydrodynamic analysis program. It provides a means for users to specify a small set of initial conditions which are then propagated through the remainder of the system. The DSSI scheme utilizes the steady-state form of the RELAP5 balance equations for nonequilibrium two-phase flow. It also employs the RELAP5 component models and constitutive model packages for wall-to-phase and interphase momentum and heat exchange. A fully implicit solution of the linearized hydrodynamic equations is implemented. An implicit coupling scheme is used to augment the standard steady-state heat conduction solution for steam generator use. It solves the primary-side tube region energy equations, heat conduction equations, wall heat flux boundary conditions, and overall energy balance equation as a coupled system of equations and improves convergence. The DSSI method for initializing RELAP5 problems to steady-state conditions has been compared with the transient solution scheme using a suite of test problems including; adiabatic single-phase liquid and vapor flow through channels with and without healing and area changes; a heated two-phase test bundle representative of BWR core conditions; and a single-loop PWR model.

Markov dynamics are the most elemental and omnipresent form of stochastic dynamics in the sciences, with applications ranging from physics to chemistry, from biology to evolution, and from economics to finance. Markov dynamics can be either stationary or nonstationary. Stationary Markov dynamics represent statistical steadystates and are quantified by stationary densities. In this paper, we generalize the notion of steadystate to the case of general Markov dynamics. Considering an ensemble of independent motions governed by common Markov dynamics, we establish that the entire ensemble attains Poissonian steadystates which are quantified by stationary Poissonian intensities and which hold valid also in the case of nonstationary Markov dynamics. The methodology is applied to a host of Markov dynamics, including Brownian motion, birth-death processes, random walks, geometric random walks, renewal processes, growth-collapse dynamics, decay-surge dynamics, Ito diffusions, and Langevin dynamics.

The successful development of multimegawatt MPD thrusters depends, to a great extent, on testing them under steadystate high altitude space conditions. Steadystate testing is required to provide thermal characteristics, life cycle, erosion, and other essential data. the major technical obstacle for ground testing of MPD thrusters in a space simulation facility is the inability of state-of-the-art vacuum systems to handle the tremendous pumping speeds required for multimegawatt MPD thrusters. This is true for other types of electric propulsion devices as well. This paper discusses the results of the first phase of an evaluation of steadystate MPD thruster test facilities. The first phase addresses the conceptual design of vacuum systems required to support multimegawatt MPD thruster testing. Three advanced pumping system concepts were evaluated and are presented here.

We report diurnal variations in 18O discrimination (18 delta) during photosynthesis (18 delta A) and respiration (18 delta R) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18 delta (18 delta pred) based on concurrent measurements of branch gas exchange to evaluate steadystate and non-steadystate (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the Delta 18O of atmospheric CO2. The non-steadystate approach substantially improved the agreement between 18 delta pred and observed 18 delta (18 delta obs) compared with the assumption of isotopic steadystate (ISS) for the Delta 18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18 delta values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of delta 18O of CO2. PMID:17087476

A constructive criterion for decoupling the steadystates of linear multivariable systems is developed. The criterion consists of n(n-1) inequalities with the type numbers of the compensator transfer functions as the unknowns. These unknowns can be chosen to satisfy the inequalities and hence achieve a steadystate decoupling scheme. It turns out that pure integrators in the loops play an important role. An extended root locus design method is then developed to take care of the stability and transient response. The overall procedure is applied to the compensation design for STOL C-8A aircraft in the approach mode.

We study the existence and properties of the non-equilibrium steadystate which arises by putting two copies of systems at different temperatures into a thermal contact. We solve the problem for the relativistic systems that are described by the energy-momentum of a perfect hydro with general equation of state (EOS). In particular, we examine several simple examples: a hydro with a linear EOS, a holographic CFT perturbed by a relevant operator and a barotropic fluid, i.e., P=P({E}) . Our studies suggest that the formation of steadystate is a universal result of the hydro regime regardless of the kind of fluid.

We propose steady-state electron transport based on coherent transfer by adiabatic passage (CTAP) in a linearly arranged triple quantum dot with leads attached to the outer dots. Its main feature is repeated steering of single electrons from the first dot to the last dot without relevant occupation of the middle dot. The coupling to leads enables a steady-state current, whose shot noise is significantly suppressed provided that the CTAP protocol performs properly. This represents an indication for the direct transfer between spatially separated dots and, thus, may resolve the problem of finding experimental evidence for the nonoccupation of the middle dot. PMID:23373941

Photoresponse data of high efficiency GaAs solar cells were analyzed using PC-1D V2.1. The approach required to use PC-1D for photoresponse data analysis, and the physical insights gained from performing the analysis are discussed. In particular, the effect of Al(x)Ga(1-x)As heteroface quality was modeled. Photoresponse or spectral quantum efficiency is an important tool in characterizing material quality and predicting cell performance. The strength of the photoresponse measurement lies in the ability to precisely fit the experimental data with a physical model. PC-1D provides a flexible platform for calculations based on these physical models.

In this paper, we investigate the existence and non-existence of non-constant positive steady-states of a diffusive predator-prey interaction system under homogeneous Neumann boundary condition. In homogeneous environment, we show that the predator-prey model with Leslie-Gower functional response has no non-constant positive solution, but the system with a general functional response may have at least one non-constant positive steady-state under some conditions.

The DYNGEN, a digital computer program for analyzing the steadystate and transient performance of turbojet and turbofan engines, is described. The DYNGEN is based on earlier computer codes (SMOTE, GENENG, and GENENG 2) which are capable of calculating the steadystate performance of turbojet and turbofan engines at design and off-design operating conditions. The DYNGEN has the combined capabilities of GENENG and GENENG 2 for calculating steadystate performance; to these the further capability for calculating transient performance was added. The DYNGEN can be used to analyze one- and two-spool turbojet engines or two- and three-spool turbofan engines without modification to the basic program. A modified Euler method is used by DYNGEN to solve the differential equations which model the dynamics of the engine. This new method frees the programmer from having to minimize the number of equations which require iterative solution. As a result, some of the approximations normally used in transient engine simulations can be eliminated. This tends to produce better agreement when answers are compared with those from purely steadystate simulations. The modified Euler method also permits the user to specify large time steps (about 0.10 sec) to be used in the solution of the differential equations. This saves computer execution time when long transients are run. Examples of the use of the program are included, and program results are compared with those from an existing hybrid-computer simulation of a two-spool turbofan.

The effects of grazing flow on the steadystate flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous faced liners were studied. The steady-state flow resistance of the ten specimens was measured using standard fluid mechanical experimental techniques. The acoustic impedance was measured using the two microphone method. The principal findings of the study are that the effects of grazing flow were measured and found to be small; small differences were measured between steady-state and acoustic resistance, and a semi-empirical model was derived that correlated the steady-state resistance data of the seven Feltmetal liners and the face sheet reactance of both the Feltmetal and Rigimesh liners.

Pilot-scale experiments have been performed to assess the ability of conventional treatment to control Cryptosporidium oocysts under steady-state conditions. The work was performed with a pilot plant that was designed to minimize flow rates and, as a result, the number of oocyst...

We consider the steadystate equations for a compressible fluid. Since we wish to solve for a range of speeds we must consider the equations in conservation form. For transonic speeds these equations are of mixed type. Hence, the usual approach is to add time derivatives to the steadystate equations and then march these equations in time. One then adds a time derivative of the density to the continuity equation, a derivative of the momentum to the momentum equation and a derivative of the total energy to the energy equation. This choice is dictated by the time consistent equations. However, since we are only interested in the steadystate this is not necessary. Thus we shall consider the possibility of adding a time derivative of the pressure to the continuity equation and similar modifications for the energy equation. This can then be generalized to adding combinations of time derivatives to each equation since these vanish in the steadystate. When using acceleration techniques such as residual smoothing, multigrid, etc. these are applied to the pressure rather than the density. Hence, the code duplicates the behavior of the incompressible equations for low speeds.

Presented is a matrix of institution types and institutional characteristics that can be used in planning for the steadystate in colleges and universities. Case studies of six institutions are presented: Harvard University, Boston University, Dartmouth College, Colorado College, University of Massachusetts/Boston, and Massachusetts Community…

The effects of curvature on steadystates of chemical catalytic reactions are investigated by studying the cases of the catalytic particle being a spherical or cylindrical shell. Existence and stability of solutions are studied. It is shown that the solutions converge to the solutions for the catalytic slab when the curvature goes to 0 in each case.

Points out that equilibrium binding and steady-state enzyme kinetics have a great deal in common and that related equations and error analysis can be cast in identical forms. Emphasizes that if one type of problem solution is taught, the other is also taught. Various methods of data analysis are evaluated. (JM)

Analyzes steady-state multiplicity in chemical reactors, focusing on the use of two mathematical tools, namely, the catastrophe theory and the singularity theory with a distinguished parameter. These tools can be used to determine the maximum number of possible solutions and the different types of bifurcation diagrams. (JN)

This fact sheet characterizes the steadystate charging behavior of a 2012 Chevy Volt. Both level 1 charging (120 volt) and level 2 charging (208 volts) is investigated. This fact sheet contains plots of efficiency, power factor, and current harmonics as vehicle charging is curtailed. Prominent current harmonics are also displayed in a histogram for various charge rates.

Bekiaris et al. (1993) explained the existence of multiple steadystates in homogeneous ternary azeotropic distillation, on the basis of the analysis of the case of infinite reflux and infinite column length (infinite number of trays). They showed that the predictions of multiple steadystates for such infinite columns have relevant implications for columns of finite length operated at finite reflux. In this article, experiments are described for the ternary homogeneous system methanol-methyl butyrate-toluene which demonstrate the existence of multiple steadystates (output multiplicities) caused by the vapor-liquid-equilibrium. The experiments on an industrial pilot column show two stable steadystates for the same feed flow rate and composition and the same set of operating parameters. The measurements are in excellent agreement with the predictions obtained for infinite columns using the {infinity}/{infinity} analysis tool as well as with stage-by-stage simulation results. These experiments represent the first published study reporting evidence for the predictions and simulations by various researchers showing that type of output multiplicities in distillation.

It is shown that the radiation field in the presently operated micromaser cavity may be squeezed when pumped with polarized atoms. The squeezing is in the steadystate field corresponding to the action similar to that of the conventional micromaser, with the effect of cavity dissipation during entire t(sub c) = tau + t(sub cav).

We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the…

We present a density functional theory (DFT) for steady-state nonequilibrium quantum systems such as molecular junctions under a finite bias. Based on the steady-state nonequilibrium statistics that maps nonequilibrium to an effective equilibrium, we show that ground-state DFT (GS-DFT) is not applicable in this case and two densities, the total electron density and the density of current-carrying electrons, are needed to uniquely determine the properties of the corresponding nonequilibrium system. A self-consistent mean-field approach based on two densities is then derived. The theory is implemented into SIESTA computational package and applied to study nonequilibrium electronic/transport properties of a realistic carbon-nanotube (CNT)/Benzene junction. Results obtained from our steady-state DFT (SS-DFT) are compared with those of conventional GS-DFT based transport calculations. We show that SS-DFT yields energetically more stable nonequilibrium steadystate, predicts significantly lower electric current, and is able to produce correct electronic structures in local equilibrium under a limiting case.

This paper describes a heat-transfer experiment that combines steady-state analysis and dynamic control. A process-water stream is circulated through two tube-in-shell heat exchangers in series. In the first, the process water is heated by steam. In the second, it is cooled by cooling water. The equipment is pilot-plant size: heat-transfer areas…

We compare results from numerical simulations of pulsatile blood flow in two patient-specific intracranial arterial networks using one-dimensional (1D) and three-dimensional (3D) models. Specifically, we focus on the pressure and flowrate distribution at different segments of the network computed by the two models. Results obtained with 1D and 3D models with rigid walls show good agreement in massflow distribution at tens of arterial junctions and also in pressure drop along the arteries. The 3D simulations with the rigid walls predict higher amplitude of the flowrate and pressure temporal oscillations than the 1D simulations with compliant walls at various segments even for small time-variations in the arterial cross-sectional areas. Sensitivity of the flow and pressure with respect to variation in the elasticity parameters is investigated with the 1Dmodel. PMID:20661645

Flow exchange between surface and ground water is of great importance be it for beneficial allocation and use of the water resources or for the proper exercise of water rights. That exchange can take place under a saturated or unsaturated flow regime. Which regimes occur depend on conditions in the vicinity of the interactive area. Withdrawals partially sustained by seepage may not bring about desaturation but greater amounts eventually will. The problem considered in this paper deals only with the steady-state case. It is meant as a first step toward a simple, yet accurate and physically based treatment of the transient situation. The primary purpose of the article is to provide simple criteria for determination of the initiation of desaturation in an aquifer originally in saturated hydraulic connection with a river or a recharge area. The extent of the unsaturated zone in the aquifer will increase with increasing withdrawals while at the same time the seepage rate from the river increases. However the seepage increase will stop once infiltration takes place strictly by gravity in the aquifer and is no longer opposed by the capillary rise from the water table below the riverbed. Following desaturation simple criteria are derived and simple analytical formulae provided to estimate the river seepage based on the position of the water table mound below the clogging layer and at some distance away from the river bank. They fully account for the unsaturated flow phenomena, including the existence of a drainage entry pressure. Two secondary objectives were to verify that (1) the assumption of uniform vertical flow through a clogging layer and that (2) the approximation of the water table mound below the seepage area as a flat surface were both reasonably legitimate. This approach will be especially advantageous for the implementation of the methodology in large-scale applications of integrated hydrologic models used for management.

Compaction of sediments is normally thought to start with grain sliding and cataclastic grain crushing. Then the ductile dissolution-precipitation creep processes take over. Modeling of this process normally neglects all collective rearrangement processes and regard simple packings of grains that slowly deform by steadystate pressure solution creep. From simple geometrical reasoning we know, however that imperfect packings of plastic grains must undergo rearrangement during compaction. Such rearrangement will drastically alter the microscopic, or "primitive processes" of compaction. Recent research has questioned the fundamental mechanisms ("primitive processes") of dissolution-precipitation creep. Do grain contacts heal or dissolve? Why is there asymmetric dissolution? Does pressure solution creep in single contacts ever reach steadystate? Can transient free face dissolution feed back on pressure solution creep in the contacts? The emerging radical change in our understanding of dissolution-precipitation creep as a dynamic, transient process is driven by new experiments and reevaluation of the fundamental theory. The same change in viewpoint is necessary on all time and length scales. I will present experiments [1-8] and simulations [9-11] of complex compaction behaviour [1], transient primitive processes of pressure solution creep in the contacts [2-4], free face dissolution [5] and crack healing [6]. I will also show that macroscopic observation of compaction shows smooth, universal behaviour [7]. Microscopic observation of compaction shows transient collective behaviour at all scales. Evidence points in the direction that compaction is dominated by transient processes with interacting instabilities. The interaction causes intermittency or switching between processes. A new, more complex theory of compaction is necessary to explain how the cooperative microscopic phenomena contribute to the simple, universal, macroscopic behaviour. 1. Uri, L., et. al., in

Steady-state and dynamic flux balance analysis (DFBA) was used to investigate the effects of metabolic model complexity and parameters on ethanol production predictions for wild-type and engineered Saccharomyces cerevisiae. Three metabolic network models ranging from a single compartment representation of metabolism to a genome-scale reconstruction with seven compartments and detailed charge balancing were studied. Steady-state analysis showed that the models generated similar wild-type predictions for the biomass and ethanol yields, but for ten engineered strains the seven compartment model produced smaller ethanol yield enhancements. Simplification of the seven compartment model to two intracellular compartments produced increased ethanol yields, suggesting that reaction localisation had an impact on mutant phenotype predictions. Further analysis with the seven compartment model demonstrated that steady-state predictions can be sensitive to intracellular model parameters, with the biomass yield exhibiting high sensitivity to ATP utilisation parameters and the biomass composition. The incorporation of gene expression data through the zeroing of metabolic reactions associated with unexpressed genes was shown to produce negligible changes in steady-state predictions when the oxygen uptake rate was suitably constrained. Dynamic extensions of the single and seven compartment models were developed through the addition of glucose and oxygen uptake expressions and transient extracellular balances. While the dynamic models produced similar predictions of the optimal batch ethanol productivity for the wild type, the single compartment model produced significantly different predictions for four implementable gene insertions. A combined deletion/overexpression/insertion mutant with improved ethanol productivity capabilities was computationally identified by dynamically screening multiple combinations of the ten metabolic engineering strategies. The authors concluded that

In geological CO{sub 2} storage projects, a cap rock is generally needed to prevent CO{sub 2} from leaking out of the storage formation. However, the injected CO{sub 2} may still encounter some discrete flow paths such as a conductive well or fault (here referred to as conduits) through the cap rock allowing escape of CO{sub 2} from the storage formation. As CO{sub 2} migrates upward, it may migrate into the surrounding formations. The amount of mass that is lost to the formation is called attenuation. This report describes a simplified model to calculate the CO{sub 2} mass flux at different locations of the conduit and the amount of attenuation to the surrounding formations. From the comparison among the three model results, we can conclude that the steady-state conduit model (SSCM) provides a more accurate solution than the PMC at a given discretization. When there is not a large difference between the permeability of the surrounding formation and the permeability of the conduits, and there is leak-off at the bottom formation (the formation immediately above the CO{sub 2} plume), a fine discretization is needed for an accurate solution. Based on this comparison, we propose to use the SSCM in the rapid prototype for now given it does not produce spurious oscillations, and is already in FORTRAN and therefore can be easily made into a dll for use in GoldSim.

We calculate the two-loop effective action of O(N) spin models on the lattice in a 1/D expansion to order 1/D2. The resulting free energy depends on β = 1/T and the order parameter Φ. It matches the high and low temperature regimes and is quite reliable close to the phase transition where it has a simple Landau expansion.

Benchmark calculations for radiation transport coupled to a material temperature equation in a 1-D slab and 1-D spherical geometry binary random media are presented. The mixing statistics are taken to be homogeneous Markov statistics in the 1-D slab but only approximately Markov statistics in the 1-D sphere. The material chunk sizes are described by Poisson distribution functions. The material opacities are first taken to be constant and then allowed to vary as a strong function of material temperature. Benchmark values and variances for time evolution of the ensemble average of material temperature energy density and radiation transmission are computed via a Monte Carlo type method. These benchmarks are used as a basis for comparison with three other approximate methods of solution. One of these approximate methods is simple atomic mix. The second approximate model is an adaptation of what is commonly called the Levermore-Pomraning model and which is referred to here as the standard model. It is shown that recasting the temperature coupling as a type of effective scattering can be useful in formulating the third approximate model, an adaptation of a model due to Su and Pomraning which attempts to account for the effects of scattering in a stochastic context. This last adaptation shows consistent improvement over both the atomic mix and standard models when used in the 1-D slab geometry but shows limited improvement in the 1-D spherical geometry. Benchmark values are also computed for radiation transmission from the 1-D sphere without material heating present. This is to evaluate the performance of the standard model on this geometry--something which has never been done before. All of the various tests demonstrate the importance of stochastic structure on the solution. Also demonstrated are the range of usefulness and limitations of a simple atomic mix formulation.

Fluorine (19F) NMR has emerged as a useful tool for characterization of slow dynamics in 19F-labeled proteins. One-dimensional (1D) 19F NMR spectra of proteins can be broad, irregular and complex, due to exchange of probe nuclei between distinct electrostatic environments; and therefore cannot be deconvoluted and analyzed in an objective way using currently available software. We have developed a Python-based deconvolution program, decon1d, which uses Bayesian information criteria (BIC) to objectively determine which model (number of peaks) would most likely produce the experimentally obtained data. The method also allows for fitting of intermediate exchange spectra, which is not supported by current software in the absence of a specific kinetic model. In current methods, determination of the deconvolution model best supported by the data is done manually through comparison of residual error values, which can be time consuming and requires model selection by the user. In contrast, the BIC method used by decond1d provides a quantitative method for model comparison that penalizes for model complexity helping to prevent over-fitting of the data and allows identification of the most parsimonious model. The decon1d program is freely available as a downloadable Python script at the project website (https://github.com/hughests/decon1d/). PMID:26241959

Steadystates and global dynamics of electrical activity in the cerebral cortex are investigated within the framework of a recent continuum model. It is shown that for a particular physiologically realistic class of models, at most three steadystates can occur, two of which are stable. The global dynamics of spatially uniform activity states is studied and it is shown that in a physiologically realistic class of models, the adiabatic dynamics is governed by a second-order differential equation equivalent to that for the motion of a Newtonian particle in a potential in the presence of friction. This result is used to derive a simplified dynamical equation in the friction-dominated limit. Solutions of these equations are compared with those of the full global dynamics equations and it is found that they are adequate for time scales longer than approximately 100 ms provided dendritic integration times are less than approximately 10 ms.

A theoretical model for describing bias-dependent transient and steady-state behaviors of dark current in amorphous selenium (a-Se) avalanche detector structures has been developed. The analytical model considers bulk thermal generation current from mid-gap sates, transient carrier depletion, and carrier injection from the electrodes incorporating avalanche multiplication. The proposed physics-based dark current model is compared with the published experimental results on three potential a-Se avalanche detector structures. The steady-state dark current is the minimum for the structures that have effective blocking layers for both holes and electrons. The transient decay time to reach a plateau decreases considerably with increasing electric field.

Ozone (O3) is a photochemical oxidant, an air pollutant and a greenhouse gas. As the main precursor of the hydroxyl radical (OH) it strongly affects the oxidation power of the atmosphere. The remote marine boundary layer (MBL) is considered an important region in terms of chemical O3 loss; however surface-based atmospheric observations are sparse and the photochemical processes are not well understood. To investigate the photochemistry under the clean background conditions of the Southern Atlantic Ocean, ship measurements of NO, NO2, O3, JNO2, J(O1D), HO2, OH, ROx and a range of meteorological parameters were carried out. The concentrations of NO and NO2 measured on board the French research vessel Marion-Dufresne (28° S-57° S, 46° W-34° E) in March 2007, are among the lowest yet observed. The data is evaluated for consistency with photochemical steadystate (PSS) conditions, and the calculations indicate substantial deviations from PSS (Φ>1). The deviations observed under low NOx conditions (5-25 pptv) demonstrate a remarkable upward tendency in the Leighton ratio (used to characterize PSS) with increasing NOx mixing ratio and JNO2 intensity. It is a paradigm in atmospheric chemistry that OH largely controls the oxidation efficiency of the atmosphere. However, evidence is growing that for unpolluted low-NOx (NO + NO2) conditions the atmospheric oxidant budget is poorly understood. Nevertheless, for the very cleanest conditions, typical for the remote marine boundary layer, good model agreement with measured OH and HO2 radicals has been interpreted as accurate understanding of baseline photochemistry. Here we show that such agreement can be deceptive and that a yet unidentified oxidant is needed to explain the photochemical conditions observed at 40°-60° S over the Atlantic Ocean.

Ozone (O3) is a photochemical oxidant, an air pollutant and a greenhouse gas. As the main precursor of the hydroxyl radical (OH) it strongly affects the oxidation power of the atmosphere. The remote marine boundary layer (MBL) is considered an important region in terms of chemical O3 loss; however surface-based atmospheric observations are sparse and the photochemical processes are not well understood. To investigate the photochemistry under the clean background conditions of the Southern Atlantic Ocean, ship measurements of NO, NO2, O3, JNO2, J(O1D), HO2, OH, ROx and a range of meteorological parameters were carried out. The concentrations of NO and NO2 measured on board the French research vessel Marion-Dufresne (28° S-57° S, 46° W-34° E) in March 2007, are among the lowest yet observed. The data is evaluated for consistency with photochemical steadystate (PSS) conditions, and the calculations indicate substantial deviations from PSS (Φ>1). The deviations observed under low NOx conditions (5-25 pptv) demonstrate a remarkable upward tendency in the Leighton ratio (used to characterize PSS) with increasing NOx mixing ratio and JNO2 intensity. It is a paradigm in atmospheric chemistry that OH largely controls the oxidation efficiency of the atmosphere. However, evidence is growing that for unpolluted low-NOx (NO + NO2) conditions the atmospheric oxidant budget is poorly understood. Nevertheless, for the very cleanest conditions, typical for the remote marine boundary layer, good model agreement with measured OH and HO2 radicals has been interpreted as accurate understanding of baseline photochemistry. Here we show that such agreement can be deceptive and that a yet unidentified oxidant is needed to explain the photochemical conditions observed at 40°-60° S over the Atlantic Ocean.

One of the objectives of NASA's High Performance Computing and Communications Program's (HPCCP) Numerical Propulsion System Simulation (NPSS) is to reduce the time and cost of generating aerothermal numerical representations of engines, called customer decks. These customer decks, which are delivered to airframe companies by various U.S. engine companies, numerically characterize an engine's performance as defined by the particular U.S. airframe manufacturer. Until recently, all numerical models were provided with a Fortran-compatible interface in compliance with the Society of Automotive Engineers (SAE) document AS681F, and data communication was performed via a standard, labeled common structure in compliance with AS681F. Recently, the SAE committee began to develop a new standard: AS681G. AS681G addresses multiple language requirements for customer decks along with alternative data communication techniques. Along with the SAE committee, the NPSS Steady-State Cycle Deck project team developed a standard Application Program Interface (API) supported by a graphical user interface. This work will result in Aerospace Recommended Practice 4868 (ARP4868). The Steady-State Cycle Deck work was validated against the Energy Efficient Engine customer deck, which is publicly available. The Energy Efficient Engine wrapper was used not only to validate ARP4868 but also to demonstrate how to wrap an existing customer deck. The graphical user interface for the Steady-State Cycle Deck facilitates the use of the new standard and makes it easier to design and analyze a customer deck. This software was developed following I. Jacobson's Object-Oriented Design methodology and is implemented in C++. The AS681G standard will establish a common generic interface for U.S. engine companies and airframe manufacturers. This will lead to more accurate cycle models, quicker model generation, and faster validation leading to specifications. The standard will facilitate cooperative work between

The possibility to drive quantum systems periodically in time offers unique ways to deeply modify their fundamental properties, as exemplified by Floquet topological insulators. It also opens the door to a variety of non-equilibrium effects. Resonant driving fields, in particular, lead to excitations which can expose the system to heating. We previously demonstrated that the analog of thermal states can be achieved and controlled in a fermionic Floquet system in the presence of phonon scattering, spontaneous emission, and an energy filtered fermionic bath. However, interactions play an important role in thermalization and present additional sources of heating. We analyze the effects of weak interactions in the presence of dissipation and the role of coherences in determining the steadystate of the driven system. Interactions generically create additional excitations and, in contrast to phonons, may sustain inter-Floquet-band coherences at steadystate.

As one kind of many body entangled states, spin squeezed states can be used to implement the high precise measurement beyond the standard quantum limit. Inspired by the novel spin squeezing scheme based on phonon-induced spin-spin interactions [S. D. Bennett et al., Phys. Rev. Lett. 110, 156402 (2013), 10.1103/PhysRevLett.110.156402], we reexamine the steady-state behaviors for the spin ensemble in diamond nanostructures by exerting a controllable microwave field. By using the phase-space approach we calculate analytically fluctuations of collective spin operators. We find that there is bistability and spin squeezing for the steady-state spin ensemble, despite the mechanical damping considered. Moreover, our work shows that bistability and spin squeezing can be controlled by microwave field and Zeeman splitting. The present scheme can be used to increase the stability of spin clocks, magnetometers, and other measurements based on spin-spin interaction in diamond nanostructures.

Transitions between nonequilibrium steadystates obey a generalized Clausius inequality, which becomes an equality in the quasistatic limit. For slow but finite transitions, we show that the behavior of the system is described by a response matrix whose elements are given by a far-from-equilibrium Green–Kubo formula, involving the decay of correlations evaluated in the nonequilibrium steadystate. This result leads to a fluctuation-dissipation relation between the mean and variance of the nonadiabatic entropy production, Δ {{s}\\text{na}} . Furthermore, our results extend—to nonequilibrium steady states—the thermodynamic metric structure introduced by Sivak and Crooks for analyzing minimal-dissipation protocols for transitions between equilibrium states.

Biological systems fundamentally exist out of equilibrium in order to preserve organized structures and processes. Many changing cellular conditions can be represented as transitions between nonequilibrium steadystates, and organisms have an interest in optimizing such transitions. Using the Hatano-Sasa Y-value, we extend a recently developed geometrical framework for determining optimal protocols so that it can be applied to systems driven from nonequilibrium steadystates. We calculate and numerically verify optimal protocols for a colloidal particle dragged through solution by a translating optical trap with two controllable parameters. We offer experimental predictions, specifically that optimal protocols are significantly less costly than naive ones. Optimal protocols similar to these may ultimately point to design principles for biological energy transduction systems and guide the design of artificial molecular machines. PMID:24386112

A simple and efficient approximation scheme to study electronic transport characteristics of strongly correlated nanodevices, molecular junctions, or heterostructures out of equilibrium is provided by steady-state cluster perturbation theory. In this work, we improve the starting point of this perturbative, nonequilibrium Green's function based method. Specifically, we employ an improved unperturbed (so-called reference) state ρ̂S, constructed as the steadystate of a quantum master equation within the Born-Markov approximation. This resulting hybrid method inherits beneficial aspects of both the quantum master equation as well as the nonequilibrium Green's function technique. We benchmark this scheme on two experimentally relevant systems in the single-electron transistor regime: an electron-electron interaction based quantum diode and a triple quantum dot ring junction, which both feature negative differential conductance. The results of this method improve significantly with respect to the plain quantum master equation treatment at modest additional computational cost.

The Center for Neutron Research (CNR) has been proposed in response to the needs - neutron flux, spectrum, and experimental facilities - that have been identified through workshops, studies, and discussions by the neutron-scattering, isotope, and materials irradiation research communities. The CNR is a major new experimental facility consisting of a reactor-based steadystate neutron source of unprecedented flux, together with extensive facilities and instruments for neutron scattering, isotope production, materials irradiation, and other areas of research.

We examine energy and particle exchange between finite-sized quantum systems and find a new form of nonequilibrium state. The exchange rate undergoes stepwise evolution in time, and its magnitude and sign dramatically change according to system size differences. The origin lies in interference effects contributed by multiply scattered waves at system boundaries. Although such characteristics are utterly different from those of true steadystate for infinite systems, Onsager's reciprocal relation remains universally valid. PMID:27627275

This paper extends Farrenkopf's analysis of a single-axis spacecraft attitude estimator using gyro and angle sensor data to include the angle output white noise of a rate-integrating gyro. Analytic expressions are derived for the steady-state pre-update and post-update angle and drift bias variances and for the state update equations. It is shown that only part of the state update resulting from the angle sensor measurement is propagated to future times.

Alkaline-earth-metal-like atoms with ultranarrow transitions open the door to a new regime of cavity quantum electrodynamics. That regime is characterized by a critical photon number that is many orders of magnitude smaller than what can be achieved in conventional systems. We show that it is possible to achieve superradiance in steadystate with such systems. We discuss the basic underlying mechanisms as well as the key experimental requirements.

Long-lived quasistationary states, associated with stationary stable solutions of the Vlasov equation, are found in systems with long-range interactions. Studies of the relaxation time in a model of N globally coupled particles moving on a ring, the Hamiltonian mean-field model (HMF), have shown that it diverges as Nγ for large N, with γ≃1.7 for some initial conditions with homogeneously distributed particles. We propose a method for identifying exact inhomogeneous steadystates in the thermodynamic limit, based on analyzing models of uncoupled particles moving in an external field. For the HMF model, we show numerically that the relaxation time of these states diverges with N with the exponent γ≃1. The method, applicable to other models with globally coupled particles, also allows an exact evaluation of the stability limit of homogeneous steadystates. In some cases, it provides a good approximation for the correspondence between the initial condition and the final steadystate.

Understanding water uptake and transport through the soil-plant continuum is vital for ecosystem management and agricultural water use. Plant water uptake under natural conditions is a non-steady transient flow controlled by root distribution, plant configuration, soil hydraulics, and climatic conditions. Despite significant progress in model development, a mechanistic description of transient water uptake has not been developed or remains incomplete. Here, based on advanced electrical network theory (RLC circuit theory), we developed a non-steadystate biophysical model to mechanistically analyze the fluctuations of uptake rates in response to water stress. We found that the non-steady-statemodel captures the nature of instantaneity and hysteresis of plant water uptake due to the considerations of water storage in plant xylem and coarse roots (capacitance effect), hydraulic architecture of leaf system (inductance effect), and soil-root contact (fuse effect). The model provides insights into the important role of plant configuration and hydraulic heterogeneity in helping plants survive an adverse environment. Our tests against field data suggest that the non-steady-statemodel has great potential for being used to interpret the smart water strategy of plants, which is intrinsically determined by stem size, leaf size/thickness and distribution, root system architecture, and the ratio of fine-to-coarse root lengths. PMID:25335512

Understanding water uptake and transport through the soil-plant continuum is vital for ecosystem management and agricultural water use. Plant water uptake under natural conditions is a non-steady transient flow controlled by root distribution, plant configuration, soil hydraulics, and climatic conditions. Despite significant progress in model development, a mechanistic description of transient water uptake has not been developed or remains incomplete. Here, based on advanced electrical network theory (RLC circuit theory), we developed a non-steadystate biophysical model to mechanistically analyze the fluctuations of uptake rates in response to water stress. We found that the non-steady-statemodel captures the nature of instantaneity and hysteresis of plant water uptake due to the considerations of water storage in plant xylem and coarse roots (capacitance effect), hydraulic architecture of leaf system (inductance effect), and soil-root contact (fuse effect). The model provides insights into the important role of plant configuration and hydraulic heterogeneity in helping plants survive an adverse environment. Our tests against field data suggest that the non-steady-statemodel has great potential for being used to interpret the smart water strategy of plants, which is intrinsically determined by stem size, leaf size/thickness and distribution, root system architecture, and the ratio of fine-to-coarse root lengths. PMID:25335512

Understanding water uptake and transport through the soil-plant continuum is vital for ecosystem management and agricultural water use. Plant water uptake under natural conditions is a non-steady transient flow controlled by root distribution, plant configuration, soil hydraulics, and climatic conditions. Despite significant progress in model development, a mechanistic description of transient water uptake has not been developed or remains incomplete. Here, based on advanced electrical network theory (RLC circuit theory), we developed a non-steadystate biophysical model to mechanistically analyze the fluctuations of uptake rates in response to water stress. We found that the non-steady-statemodel captures the nature of instantaneity and hysteresis of plant water uptake due to the considerations of water storage in plant xylem and coarse roots (capacitance effect), hydraulic architecture of leaf system (inductance effect), and soil-root contact (fuse effect). The model provides insights into the important role of plant configuration and hydraulic heterogeneity in helping plants survive an adverse environment. Our tests against field data suggest that the non-steady-statemodel has great potential for being used to interpret the smart water strategy of plants, which is intrinsically determined by stem size, leaf size/thickness and distribution, root system architecture, and the ratio of fine-to-coarse root lengths.

One of ITER goals is to demonstrate feasibility of continuous operations using non-inductive current drive. Two main candidates have been identified for advanced operations: the long duration, high neutron fluency hybrid scenario and the steadystate scenario, both operating at a plasma current lower than the reference ELMy scenario [1][2] to minimize the required current drive. The steadystate scenario targets plasmas with current 7-10 MA in the flat-top, 50% of which will be provided by the self-generated, pressure-driven bootstrap current. It has been estimated that, in order to obtain a fusion gain Q > 5 at a current of 9 MA, it should be ΒN > 2.5 and H > 1.5 [3]. This implies the presence of an Internal Transport Barrier (ITB). This work discusses how the stability of steadystate scenarios with ITBs is affected by the external heating sources and by perturbations of the equilibrium profiles.

Numerical solutions to the time-dependent kinetic equation, which describes the transport of superthermal electrons in the splasmasphere between the two conjugate ionospheres, are presented. The model calculates the distribution function as a function of time, field-aligned distance, energy, and pitch-angle. The processes of refilling, depleting, and establishing steady-state conditions of superthermal electrons in the plasmasphere are discussed.

Evaluation of resonant loop antenna designs for ICRF heating of plasmas requires information concerning the electrical characteristics of the structure. Our 2-D steadystatemodel described herein provides us with current strap inductance and capacitance, surface current distributions, and flux linkage to the plasma. These are used to determine the current and voltage requirements, ohmic dissipation, frequency limits and matching requirements, maximum electric fields, and plasma loading in order to compare antenna designs.

Oak Ridge National Laboratory (ORNL) is a leader in the development of analytical tools for the design of electrically driven, air-to-air heat pumps. Foremost among these tools is the ORNL Heat Pump Design Model, which can be used to predict the steady-state heating and cooling performance of an electrically driven, air-source heat pump. This version is three to five times faster than the earlier version, easier to use and more versatile.

A steady-state scheme for data assimilation in the context of a single, short period (relative to a day), sun-synchronous, polar-orbiting satellite is examined. If the satellite takes observations continuously, the gains, which are the weights for blending observations and predictions together, are steady in time. For a linear system forced by random noise, the optimal steady-state gains (Wiener gains) are equivalent to those of a Kalman filter. Computing the Kalman gains increases the computational cost of the model by a large factor, but computing the Wiener gains does not. The latter are computed by iteration using prior estimates of the gains to assimilate simulated observations of one run of the model, termed 'truth' into another run termed 'prediction'. At each stage, the prediction errors form the basis for the next estimate of the gains. Steadystate is achieved after three or four iterations. Further simplification is achieved by making the gains depend on longitudinal distance from the observation point, not on absolute longitude. For a single-layer primitive equation model, the scheme works well even if only the mass field is observed but not the velocity field. Although the scheme was developed for Mars Observer, it should be applicable to data retrieved from Earth atmosphere satellites, for example, UARS.

In this paper, we propose two methods to carry out the quasi-steadystate approximation in stochastic models of enzyme catalytic regulation, based on WKB asymptotics of the chemical master equation or of the corresponding partial differential equation for the generating function. The first of the methods we propose involves the development of multiscale generalisation of a WKB approximation of the solution of the master equation, where the separation of time scales is made explicit which allows us to apply the quasi-steadystate approximation in a straightforward manner. To the lowest order, the multi-scale WKB method provides a quasi-steadystate, Gaussian approximation of the probability distribution. The second method is based on the Hamilton-Jacobi representation of the stochastic process where, as predicted by large deviation theory, the solution of the partial differential equation for the corresponding characteristic function is given in terms of an effective action functional. The optimal transition paths between two states are then given by those paths that maximise the effective action. Such paths are the solutions of the Hamilton equations for the Hamiltonian associated to the effective action functional. The quasi-steadystate approximation is applied to the Hamilton equations thus providing an approximation to the optimal transition paths and the transition time between two states. Using this approximation we predict that, unlike the mean-field quasi-steady approximation result, the rate of enzyme catalysis depends explicitly on the initial number of enzyme molecules. The accuracy and validity of our approximated results as well as that of our predictions regarding the behaviour of the stochastic enzyme catalytic models are verified by direct simulation of the stochastic model using Gillespie stochastic simulation algorithm. PMID:24832255

In this paper, we propose two methods to carry out the quasi-steadystate approximation in stochastic models of enzyme catalytic regulation, based on WKB asymptotics of the chemical master equation or of the corresponding partial differential equation for the generating function. The first of the methods we propose involves the development of multiscale generalisation of a WKB approximation of the solution of the master equation, where the separation of time scales is made explicit which allows us to apply the quasi-steadystate approximation in a straightforward manner. To the lowest order, the multi-scale WKB method provides a quasi-steadystate, Gaussian approximation of the probability distribution. The second method is based on the Hamilton-Jacobi representation of the stochastic process where, as predicted by large deviation theory, the solution of the partial differential equation for the corresponding characteristic function is given in terms of an effective action functional. The optimal transition paths between two states are then given by those paths that maximise the effective action. Such paths are the solutions of the Hamilton equations for the Hamiltonian associated to the effective action functional. The quasi-steadystate approximation is applied to the Hamilton equations thus providing an approximation to the optimal transition paths and the transition time between two states. Using this approximation we predict that, unlike the mean-field quasi-steady approximation result, the rate of enzyme catalysis depends explicitly on the initial number of enzyme molecules. The accuracy and validity of our approximated results as well as that of our predictions regarding the behaviour of the stochastic enzyme catalytic models are verified by direct simulation of the stochastic model using Gillespie stochastic simulation algorithm.

Type 1 diabetes (T1D) is often triggered by a viral infection, but the T1D prevalence is rising among populations that have a lower exposure to viral infection. In an animal model of T1D, the NOD mouse, viral infection at different ages may either accelerate or delay disease depending on the age of infection and the type of virus. Viral infection may affect the progression of T1D via multiple mechanisms: triggering inflammation, bystander activation of self-reactive T-cells, inducing a competitive immune response, or inducing a regulatory immune response. In this paper, we create mathematical models of the interaction of viral infection with T1D progression, incorporating each of these four mechanisms. Our goal is to understand how each viral mechanism interacts with the age of infection. The model predicts that each viral mechanism has a unique pattern of interaction with disease progression. Viral inflammation always accelerates disease, but the effect decreases with age of infection. Bystander activation has little effect at younger ages and actually decreases incidence at later ages while accelerating disease in mice that do get the disease. A competitive immune response to infection can decrease incidence at young ages and increase it at older ages, with the effect decreasing over time. Finally, an induced Treg response decreases incidence at any age of infection, but the effect decreases with age. Some of these patterns resemble those seen experimentally. PMID:27030351

This paper investigates the steady-state responses of a rotor system supported by auxiliary bearings in which there is a clearance between the rotor and the inner race of the bearing. A simulation model based upon the rotor of a production jet engine is developed and its steady-state behavior is explored over a wide range of operating conditions for various parametric configurations. Specifically, the influence of rotor imbalance, clearance, support stiffness and damping is studied. Bifurcation diagrams are used as a tool to examine the dynamic behavior of this system as a function of the afore mentioned parameters. The harmonic balance method is also employed for synchronous response cases. The observed dynamical responses is discussed and some insights into the behavior of such systems are presented.

Optimality principles have been used for investigating physical processes in different areas. This work attempts to apply an optimal principle (that water flow resistance is minimized on global scale) to steady-state unsaturated flow processes. Based on the calculus of variations, we show that under optimal conditions, hydraulic conductivity for steady-state unsaturated flow is proportional to a power function of the magnitude of water flux. This relationship is consistent with an intuitive expectation that for an optimal water flow system, locations where relatively large water fluxes occur should correspond to relatively small resistance (or large conductance). Similar results were also obtained for hydraulic structures in river basins and tree leaves, as reported in other studies. Consistence of this theoretical result with observed fingering-flow behavior in unsaturated soils and an existing model is also demonstrated.

The contribution presents a comparison of a runoff simulated by profile method (1D) and spatially distributed method (2D). Simulation model SMODERP is used for calculation and prediction of soil erosion and surface runoff from agricultural land. SMODERP is physically based model that includes the processes of infiltration (Phillips equation), surface runoff (kinematic wave based equation), surface retention, surface roughness and vegetation impact on runoff. 1Dmodel was developed in past, new 2D model was developed in last two years. The model is being developed at the Department of Irrigation, Drainage and Landscape Engineering, Civil Engineering Faculty, CTU in Prague. 2D model was developed as a tool for widespread GIS software ArcGIS. The physical relations were implemented through Python script. This script uses ArcGIS system tools for raster and vectors treatment of the inputs. Flow direction is calculated by Steepest Descent algorithm in the preliminary version of 2D model. More advanced multiple flow algorithm is planned in the next version. Spatially distributed models enable to estimate not only surface runoff but also flow in the rills. Surface runoff is described in the model by kinematic wave equation. Equation uses Manning roughness coefficient for surface runoff. Parameters for five different soil textures were calibrated on the set of forty measurements performed on the laboratory rainfall simulator. For modelling of the rills a specific sub model was created. This sub model uses Manning formula for flow estimation. Numerical stability of the model is solved by Courant criterion. Spatial scale is fixed. Time step is dynamically changed depending on how flow is generated and developed. SMODERP is meant to be used not only for the research purposes, but mainly for the engineering practice. We also present how the input data can be obtained based on available resources (soil maps and data, land use, terrain models, field research, etc.) and how can

Breast thermography still has inherent limitations that prevent it from being fully accepted as a breast screening modality in medicine. The main challenges of breast thermography are to reduce false positive results and to increase the sensitivity of a thermogram. Further, it is still difficult to obtain information about tumour parameters such as metabolic heat, tumour depth and diameter from a thermogram. However, infrared technology and image processing have advanced significantly and recent clinical studies have shown increased sensitivity of thermography in cancer diagnosis. The aim of this paper is to study numerically the possibilities of extracting information about the tumour depth from steadystate thermography and transient thermography after cold stress with no need to use any specific inversion technique. Both methods are based on the numerical solution of Pennes bioheat equation for a simple three-dimensional breast model. The effectiveness of two approaches used for depth detection from steadystate thermography is assessed. The effect of breast density on the steadystate thermal contrast has also been studied. The use of a cold stress test and the recording of transient contrasts during rewarming were found to be potentially suitable for tumour depth detection during the rewarming process. Sensitivity to parameters such as cold stress temperature and cooling time is investigated using the numerical model and simulation results reveal two prominent depth-related characteristic times which do not strongly depend on the temperature of the cold stress or on the cooling period. PMID:26522612

Several independent observations have suggested that the catastrophe transition in microtubules is not a first-order process, as is usually assumed. Recent in vitro observations by Gardner et al. [M. K. Gardner et al., Cell 147, 1092 (2011), 10.1016/j.cell.2011.10.037] showed that microtubule catastrophe takes place via multiple steps and the frequency increases with the age of the filament. Here we investigate, via numerical simulations and mathematical calculations, some of the consequences of the age dependence of catastrophe on the dynamics of microtubules as a function of the aging rate, for two different models of aging: exponential growth, but saturating asymptotically, and purely linear growth. The boundary demarcating the steady-state and non-steady-state regimes in the dynamics is derived analytically in both cases. Numerical simulations, supported by analytical calculations in the linear model, show that aging leads to nonexponential length distributions in steadystate. More importantly, oscillations ensue in microtubule length and velocity. The regularity of oscillations, as characterized by the negative dip in the autocorrelation function, is reduced by increasing the frequency of rescue events. Our study shows that the age dependence of catastrophe could function as an intrinsic mechanism to generate oscillatory dynamics in a microtubule population, distinct from hitherto identified ones.

Linear quadratic (LQ) bumpless transfer design introduced recently by Turner and Walker gives a very convenient and straightforward computational procedure for the steady-state bumpless transfer operator synthesis. It is, however, found to be incapable of providing convergence of the output of the offline controller to that of the online controller in several industrial applications, producing bumps in the plant output in the wake of controller transfer. An examination of this phenomenon reveals that the applications in question are characterized by a significant mismatch, further referred to as controller uncertainty, between the dynamics of the implemented controllers and their models used in the transfer operator computation. To address this problem, while retaining the convenience of the Turner and Walker design, a novel state/output feedback bumpless transfer topology is introduced that employs the nominal state of the offline controller and, through the use of an additional controller/model mismatch compensator, also the offline controller output. A corresponding steady-state bumpless transfer design procedure along with the supporting theory is developed for a large class of systems. Due to these features, it is demonstrated to solve a long-standing problem of high-quality steady-state bumpless transfer from the industry standard low-order nonlinear multiloop PID-based controllers to the modern multiinput-multioutput (MIMO) robust controllers in the megawatt/throttle pressure control of a typical coal-fired boiler/turbine unit.

After a decision by the ITER parties to investigate the possibility of designing a reduced cost version of ITER several possible machine layouts with different aspect ratios were studied. Relatively early in this process it became clear that there is no significant cost difference between different aspect ratios and that there is a maximum realistically possible aspect ratio for a machine with 6 m major radius and rather high plasma shaping. Following this study a machine with an intermediate aspect ratio (3.1) called the ITER Fusion Energy Advanced Tokamak (ITER FEAT) was chosen as the basis for the outline design of a reduced cost ITER. Several potential steadystate scenarios can be investigated in ITER FEAT, i.e. monotonic or reversed shear at full or reduced minor radius. In addition, so-called hybrid discharges, are feasible where a mixture of inductive and non-inductive current drive as well as bootstrap current allows long pulse discharges of the order of 2500 s. The βN values and H factors required for these discharges are in the same range as those observed on present machines, which provides confidence that such discharges can be studied in ITER FEAT. However, due to uncertainties in physics knowledge, for example the current drive efficiency off-axis, it is impossible at present to generate a completely self-consistent scenario taking all boundary conditions, for example engineering or heating system constraints, into account. In addition, all of these regimes have a potential problem with divertor operation compatibility (low edge density) and with helium exhaust which has to be addressed in existing experiments. For the engineering design of the in-vessel components and for the balance of the plant there is practically no difference between inductive (500 s) and steadystate operation. However, the choice of heating systems and the distribution of power between them will be strongly influenced by the envisaged steadystate scenarios.

We show that short-range correlations have a dramatic impact on the steady-state phase diagram of quantum driven-dissipative systems. This effect, never observed in equilibrium, follows from the fact that ordering in the steadystate is of dynamical origin, and is established only at very long times, whereas in thermodynamic equilibrium it arises from the properties of the (free) energy. To this end, by combining the cluster methods extensively used in equilibrium phase transitions to quantum trajectories and tensor-network techniques, we extend them to nonequilibrium phase transitions in dissipative many-body systems. We analyze in detail a model of spin-1 /2 on a lattice interacting through an X Y Z Hamiltonian, each of them coupled to an independent environment that induces incoherent spin flips. In the steady-state phase diagram derived from our cluster approach, the location of the phase boundaries and even its topology radically change, introducing reentrance of the paramagnetic phase as compared to the single-site mean field where correlations are neglected. Furthermore, a stability analysis of the cluster mean field indicates a susceptibility towards a possible incommensurate ordering, not present if short-range correlations are ignored.

We consider a dynamical model for superfluid Fermi gas, trapped in the central well of an axially symmetric Bessel optical lattice potential. The equation includes nonlinear power-law form of the chemical potential μ(n) = C|ψ|2γ, for γ = 2 3, which accounts for Fermi pressure. Reducing the equation to two-dimensional (2D) form, we obtain the basic steadystate solutions of the system along the Bose-Einstein condensation (BEC) side to Bardeen-Cooper-Schrieffer (BCS) side by employing the energy balance condition, which are guided by the variational approximation. It is found that the strength ɛ and the radial scale r of the Bessel optical lattice have an extreme effect on the characters of basic steadystate solution. Analytically, we deduce the atomic density distribution, the average atom number and the average energy of basic steadystate, where the atom distribution of the system presents on periodic change with r, and increases faster at unitarity than in the BEC limit. Furthermore, because of the Fermi pressure, the atomic density distribution at the unitarity is more extensive than that in the BEC limit. In particular, there exist very interesting changes, the average energy intends to collapse state with r, however it emerges as a stable state with varying L both in the BEC limit and at unitarity.

In this work we analyze the validity of Lifshitz's theory for the case of nonequilibrium scenarios from a full quantum dynamical approach. We show that Lifshitz's framework for the study of the Casimir pressure is the result of considering the long-time regime (or steadystate) of a well-defined fully quantized problem, subjected to initial conditions for the electromagnetic field interacting with real materials. For this, we implement the closed time path formalism developed in previous works to study the case of two half spaces (modeled as composite environments, consisting in quantum degrees of freedom plus thermal baths) interacting with the electromagnetic field. Starting from initial uncorrelated free subsystems, we solve the full time evolution, obtaining general expressions for the different contributions to the pressure that take part on the transient stage. Using the analytic properties of the retarded Green functions, we obtain the long-time limit of these contributions to the total Casimir pressure. We show that, in the steadystate, only the baths' contribute, in agreement with the results of previous works, where this was assumed without justification. We also study in detail the physics of the initial conditions' contribution and the concept of modified vacuum modes, giving insights about in which situations one would expect a nonvanishing contribution at the steadystate of a nonequilibrium scenario. This would be the case when considering finite width slabs instead of half-spaces.

Skeletal muscle contraction during ischemia, such as that experienced by peripheral vascular disease patients, is characterized by rapid fatigue. Using a canine gracilis model, we tested the hypothesis that a critical factor determining force production during ischemia is the metabolic response during the transition from rest to steadystate. Dichloroacetate (DCA) administration before gracilis muscle contraction increased pyruvate dehydrogenase complex activation and resulted in acetylation of 80% of the free carnitine pool to acetylcarnitine. After 1 min of contraction, phosphocreatine (PCr) degradation in the DCA group was approximately 50% lower than in the control group (P < 0.05) during conditions of identical force production. After 6 min of contraction, steady-state force production was approximately 30% higher in the DCA group (P < 0.05), and muscle ATP, PCr, and glycogen degradation and lactate accumulation were lower (P < 0.05 in all cases). It appears, therefore, that an important determinant of contractile function during ischemia is the mechanisms by which ATP regeneration occurs during the period of rest to steady-state transition. PMID:9277374

We develop two general methods to infer the gravitational potential of a system using steady-state tracers, i.e. tracers with a time-independent phase-space distribution. Combined with the phase-space continuity equation, the time independence implies a universal orbital probability density function (oPDF) dP(λ|orbit) ∝ dt, where λ is the coordinate of the particle along the orbit. The oPDF is equivalent to Jeans theorem, and is the key physical ingredient behind most dynamical modelling of steady-state tracers. In the case of a spherical potential, we develop a likelihood estimator that fits analytical potentials to the system and a non-parametric method (`phase-mark') that reconstructs the potential profile, both assuming only the oPDF. The methods involve no extra assumptions about the tracer distribution function and can be applied to tracers with any arbitrary distribution of orbits, with possible extension to non-spherical potentials. The methods are tested on Monte Carlo samples of steady-state tracers in dark matter haloes to show that they are unbiased as well as efficient. A fully documented C/PYTHON code implementing our method is freely available at a GitHub repository linked from http://icc.dur.ac.uk/data/#oPDF.

An adaptive controller for stabilization of unknown unstable steadystates (spirals, nodes and saddles) of nonlinear dynamical systems is considered and its robustness under the changes of the location of the fixed point in the phase space is demonstrated. An analog electronic controller, based on a low-pass filter technique, is described. It can be easily switched between a stable and an unstable mode of operation for stabilizing either spirals/nodes or saddles, respectively. Numerical and experimental results for two autonomous systems, the damped Duffing-Holmes oscillator and the chaotic Lorenz system, are presented.

A fluid-structure interaction code, ENSAERO, has been used to compute the aerodynamic loads on a swept-tapered wing. The code has the capability of using Euler or Navier-Stokes equations. Both options have been used and compared in the present paper. In the calculation of the steady-state solution, we are interested in knowing how the flexibility of the wing influences the lift coefficients. If the results of a flexible wing are not affected by the flexibility of the wing significantly, one could consider the wing to be rigid and reduce the problem from fluid-structure interaction to a fluid problem.

NASA Glenn Research Center at Lewis Field designed and developed a steadystate vacuum ultraviolet automated (SSVUVa) facility with in situ VUV intensity calibration capability. The automated feature enables a constant accelerated VUV radiation exposure over long periods of testing without breaking vacuum. This test facility is designed to simultaneously accommodate four isolated radiation exposure tests within the SSVUVa vacuum chamber. Computer-control of the facility for long, term continuous operation also provides control and recording of thermocouple temperatures, periodic recording of VUV lamp intensity, and monitoring of vacuum facility status. This paper discusses the design and capabilities of the SSVUVa facility.

The experimental programme of Tore Supra is devoted to the study of technology and physics issues associated to long-duration high performance discharges. This new domain of operation requires simultaneously and in steadystate: heat removal capability, particle exhaust, fully non-inductive current drive, advanced technology integration and real time plasma control. The long discharge allows for addressing new time scale physic such as the wall particle retention and erosion. Moreover, the physics of fully non-inductive discharges is full of novelty, namely: the MHD stability, the slow spontaneous oscillation of the central electron temperature or the outstanding inward particle pinch.

Ergodic mixing is prerequisite to any statistical-mechanical calculation of properties derived from atomistic dynamical simulations. Thus the time-reversible thermostats and ergostats used in simulating Gibbsian equilibrium dynamics or nonequilibrium steady-state dynamics should impose ergodicity and mixing. Though it is hard to visualize many-dimensional phase-space distributions, recent developments provide several practical numerical approaches to the problem of ergodic mixing. Here we apply three of these approaches to a useful nonequilibrium test problem, an oscillator in a temperature gradient. {copyright} {ital 1997} {ital The American Physical Society}

A desktop program is developed in Microsoft EXCEL using Visual Basic for Applications (VBA) to solve a two-dimensional steadystate heat conduction problem with a radiation boundary condition. The resulting partial differential equation and boundary conditions are solved using finite difference techniques and the results are compared with a finite element solution using the commercially available software package MSC/THERMAL. The results from the two methods are found to be within 1 percent. The VBA solution demonstrates how spreadsheet programs, like EXCEL, can be used to solve practical engineering problems with good accuracy.

Partial difference equation plays important role in simulating a wide variety of science and engineering problem. In this paper, we develop numerical application which implements the iterative methods for steadystate simulation and its numerical engine. A new approach names Alternate Left Right is applied onto Successive Overrelaxation (SOR) called as the Alternate Left Right Successive Overrelaxation (ALRSOR) iterative method. The experiment's results are compared amongst SOR and ALRSOR to reveal the performance of these numerical engines. From the results, Alternate Left Right approach successfully increases the speed computation. In conclusion, ALRSOR method performs the fastest amongst the compared method.

A skewness of the probability for instantaneous current fluctuations, in a nonequilibrium steadystate, is observed experimentally in a dusty plasma. This skewness is attributed to the spatial asymmetry, which is imminent to the nonequilibrium systems due to the external hydrodynamic gradient. Using the modern framework of the large deviation theory, we extend the Onsager-Machlup ansatz for equilibrium fluctuations to systems with a preferred spatial direction, and provide a modulated Gaussian probability distribution, which is tested by simulations. This probability distribution is also of potential interest for other statistical disciplines. Connections with the principles of statistical mechanics, due to Boltzmann and Gibbs, are discussed as well.

A variety of methods are available for estimating aquifer recharge in semi-arid regions, each with advantages and disadvantages. We are investigating a procedure for estimating recharge in an irrigated basin. The method involves computing irrigation return flows based on HYDRUS-1Dmodeling of root z...

The territory of Montenegro and its vicinity are characterized by high-seismicity rate and very complex tectonics. Namely, southern Adria microplate subducts beneath Eurasia, forming the Dinarides fold-and-thrust belt which spreads through whole Montenegro and the western Balkans. Present-day lithosphere structure of the Adria-Dinarides collision zone in general is not constrained very well and, consequently, there is a lack of three-dimensional (3D) velocity models in this region. For these reasons, high resolution 3D tomography modeling of this area is considered to be of great importance. As part of preparatory phase for conducting a 3D local earthquake tomography study, a substantial amount of waveform data was collected, from all surroundings national seismic networks including 130 seismic stations from 11 countries. The data set comprises waveforms from 1452 earthquakes in the region recorded during time period 1990 - 2014. The collected data were obtained in different formats and the data base was harmonized by converting and integrating all data to miniseed format. The potential resolution of collected data for seismic tomography purpose was analyzed by ray density testing, using specially developed software for this specific purpose. The result is expressed as the number of rays between selected group of earthquake hypocenters and seismic stations, penetrating through the 3D model of the Earth crust and it documents the great potential of the data set for 3D seismic tomography. As a prerequisite to 3D tomography and for consistent high-precision earthquake locations, a minimum 1D velocity model has been calculated. The data set of around 400 earthquakes was selected from the main database and consistent wave onsets picking was performed, including seismic phase interpretation and its quality assessment. This highly consistent travel time data set is used for calculation of 1D velocity models for the region under study. The minimum 1Dmodels were derived

NEWT1D, a one dimensional multifluid model of the scrape-off layer and divertor plasma, has been used to model the plasma including the distribution of carbon ionization states in the SOL and divertor of ELMing H-mode at two injected power levels in DIII-D. Comparison of the code predictions to the measured divertor and scrape-off layer (SOL) plasma density and temperature shows good agreement. Comparison of the predicted line emissions to the spectroscopic data suggests that physically sputtered carbon from the strike point is not transported up the flux tube; a distributed source of carbon a few centimeters up the flux tube is required to achieve reasonable agreement.

Sharp interface methods have been used successfully to describe the physics of upconing. A finite-element model is developed to simulate a sharp interface for determination of the steady-state position of the interface and maximum permissible well discharges. The model developed is compared to previous published electric-analog model results of Bennett and others (1968). -from Authors

Research on nucleate pool boiling in microgravity using R-113 as a working fluid was conducted using a five-second drop tower and five space flights at a/g approximately 10(-4). A 19 x 38-mm flat gold film heater was used that allowed cine camera viewing both from the side and the bottom of the heater. It was concluded that for both subcooled and saturated liquids long-term steady-state pool boiling can take place in reduced gravity, but the effectiveness of the boiling heat transfer appears to depend on the heater geometry and on the size and the properties of fluids. Heat transfer is enhanced at lower heat flux levels and the CHF increases as the subcooling increases. It was found that several mechanisms are responsible for the steady-state nucleate pool boiling in the absence of buoyancy. The mechanisms considered here are defined and summarized as bubble removal, bubble coalescence, thermocapillary flow, bubble migration, and latent heat transport. PMID:12446341

We ask what happens when two nonequilibrium systems in steadystate are kept in contact and allowed to exchange a quantity, say mass, which is conserved in the combined system. Will the systems eventually evolve to a new stationary state where a certain intensive thermodynamic variable, like equilibrium chemical potential, equalizes following the zeroth law of thermodynamics and, if so, under what conditions is it possible? We argue that an equilibriumlike thermodynamic structure can be extended to nonequilibrium steadystates having short-ranged spatial correlations, provided that the systems interact weakly to exchange mass with rates satisfying a balance condition—reminiscent of a detailed balance condition in equilibrium. The short-ranged correlations would lead to subsystem factorization on a coarse-grained level and the balance condition ensures both equalization of an intensive thermodynamic variable as well as ensemble equivalence, which are crucial for construction of a well-defined nonequilibrium thermodynamics. This proposition is proved and demonstrated in various conserved-mass transport processes having nonzero spatial correlations.

The pseudospectral three-dimensional MHD code of Dahlburg et al. (1986 and 1987) is used to compute the dynamical behavior of a channel of magnetofluid carrying an axial current and magnetic flux. This situation contains the essential MHD behavior of the reversed-field pinch (RFP). An externally imposed electric field is applied to an initially current-free magnetofluid and drives currents that rise and eventually fluctuate about values corresponding to pinch ratios Theta of about 1.3, 2.2, and 4.5. A period of violent turbulence leads to an approximately force-free core, surrounded by an active MHD boundary layer that is not force-free. A steadystate is reached that can apparently be sustained indefinitely (for several hundred Alfven transit times or longer). The turbulence level and time variability in the steadystate increase with increasing Theta. The average toroidal magnetic field at the wall reverses for Theta = 2.2 and 4.5, but not for Theta = 1.3. Negative toroidal current filaments are observed. The Lundquist numbers are of the order of a few hundred.

A friction and wear study was made at 20 C to obtain improved reproducibility and reliability in boundary lubrication testing. Ester-base and C-ether-base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a friction and wear apparatus. Conditions included loads of 1/2 and 1 kg and sliding velocities of 3.6 to 18.2 m/min in a dry air atmosphere and stepwise time intervals from 1 to 250 min for wear measurements. The wear rate results were compared with those from previous studies where a single 25 min test period was used. Satisfactory test conditions for studying friction and wear in boundary lubrication for this apparatus were found to be 1 kg load; sliding velocities of 7.1 to 9.1 m/min (50 rpm disk speed); and use of a time stepwise test procedure. Highly reproducible steady-state wear rates and steady-state friction coefficients were determined under boundary conditions. Wear rates and coefficients of friction were constant following initially high values during run-in periods.

Enceladus is one of the most geologically active bodies in the Solar System. The satellite's diverse surface suggests that Enceladus was subject to past episodic heating. It is largely probable that the activity of Enceladus is not in a steadystate. In order to analyze the non-steadystate heating, thermal and orbital coupled calculation is needed because they affect each other. We perform the coupled calculation assuming conductive ice layer and low melting temperature. Although the heating state of Enceladus strongly depends on the rheological parameters used, episodic heating is induced if the Q-value of Saturn is less than 23,000 and Enceladus' core radius is less than 161 km. The duration of one episodic heating cycle is around one hundred million years. The cyclic change in ice thickness is consistent with the origin of a partial ocean which is suggested by plume emissions and diverse surface states of Enceladus. Although the obtained tidal heating rate is smaller than the observed heat flux of a few giga watt, other heating mechanisms involving e.g., liquid water and/or specific chemical reactions may be initiated by the formation of a partial or global subsurface ocean.

A set of graphics with explanations illustrating gas turbine engine steadystate behavior are presented. Typical combinations of compressors and nozzles which occur in a gas turbine engine are shown. The basic effect of a nozzle is explained by considering a compressor on a test rig: typical compressor, fan, and turbine characteristics are illustrated. The following are discussed: the degrees of freedom of an aeroengine (the flow and the power); the 'working lines' of components (the locus of the off design steadystate operating points of a component plotted on a chart of that components characteristics); bleed and whirl; offtakes; P1 effects (performance changes which modify the basic nondimensional behavior an engine (caused by the effect on Reynolds number levels and on engine mechanical configuration of basic engine inlet pressure level)), and T1 effects (performance changes which modify the basic nondimensional behavior of an engine and are caused by the effects of engine inlet temperature level on Reynolds number level, on engine mechanical configuration and on specific heat level); variable nozzles; and turbojet matching.

The two objectives of this paper are to describe a steady-state version of the Age-Layered Population Structure (ALPS) Evolutionary Algorithm (EA) and to compare it against other GAs on real-valued problems. Motivation for this work comes from our previous success in demonstrating that a generational version of ALPS greatly improves search performance on a Genetic Programming problem. In making steady-state ALPS some modifications were made to the method for calculating age and the method for moving individuals up layers. To demonstrate that ALPS works well on real-valued problems we compare it against CMA-ES and Differential Evolution (DE) on five challenging, real-valued functions and on one real-world problem. While CMA-ES and DE outperform ALPS on the two unimodal test functions, ALPS is much better on the three multimodal test problems and on the real-world problem. Further examination shows that, unlike the other GAs, ALPS maintains a genotypically diverse population throughout the entire search process. These findings strongly suggest that the ALPS paradigm is better able to avoid premature convergence then the other GAs.

The evolution of orogens is highly affected by surface processes that control mass distribution. Transportation and redistribution of mass at the Earth's surface modifies the gravitational load and alters the stress field and kinematics within orogens. We explore the role of asymmetric erosion, indenter dip angle, and flux steady/non-steadystate in determining the patterns of deformation and exhumation in doubly-sided orogenic wedges. In our analogue model, shortening of the orogen is driven by rigid indenters, represented by Plexiglas wedged blocks (35 and 70 degrees) that deform a non-cohesive dry Coulomb material (walnut shells) representing crustal material. Three end-member erosional scenarios are considered. In the first case, erosion is not applied, and thus the doubly-sided orogenic wedge evolves without restraints (non-steadystate). In the second case, erosion is concentrated solely on the indenters side of the orogen (retrowedge), and in the third case, erosion is focused on the flank opposite to the indenter side (prowedge). In the last two cases, steady-state conditions were present in the middle stages of shortening. Strain and exhumation were calculated using displacement fields from 2D particle image velocimetry (PIV analysis). In the three cases, the model deforms as a combination of lateral compaction and localization of strain in shear bands. In the early stages of deformation, a "pop-up" structure develops, bounded by a fore-shear on the front and a back-shear toward the indenter. As deformation continues, a new fore-shear develops, and the previous one remains inactive and is passively pushed up the wedge. In the case of no erosion, the old fore-shears rotate slightly toward the indenter, and the shear bands evolve to steeply dipping structures. In the case of retrowedge erosion, the old fore-shears back rotate toward the indenter, and the shear bands evolve to shallowly dipping structures. In the case of prowedge erosion, old fore

Prostate-specific antigen (PSA), an enzyme of 30 kDa grouped in the kallikrein family is synthesized to high levels by normal and malignant prostate epithelial cells. Therefore, it is the main biomarker currently used for early diagnosis of prostate cancer. Here, presteady-state and steady-state kinetics of the PSA-catalyzed hydrolysis of the fluorogenic substrate Mu-His-Ser-Ser-Lys-Leu-Gln-AMC (spanning from pH 6.5 to pH 9.0, at 37.0°C) are reported. Steady-state kinetics display at every pH value a peculiar feature, represented by an initial “burst” phase of the fluorescence signal before steady-state conditions are taking place. This behavior, which has been already observed in other members of the kallikrein family, suggests the occurrence of a proteolytic mechanism wherefore the acylation step is faster than the deacylation process. This feature allows to detect the acyl intermediate, where the newly formed C-terminal carboxylic acid of the cleaved substrate forms an ester bond with the -OH group of the Ser195 catalytic residue, whereas the AMC product has been already released. Therefore, the pH-dependence of the two enzymatic steps (i.e., acylation and deacylation) has been separately characterized, allowing the determination of pKa values. On this basis, possible residues are tentatively identified in PSA, which might regulate these two steps by interacting with the two portions of the substrate. PMID:25068395

Background Zero-dimensional (lumped parameter) and one dimensional models, based on simplified representations of the components of the cardiovascular system, can contribute strongly to our understanding of circulatory physiology. Zero-D models provide a concise way to evaluate the haemodynamic interactions among the cardiovascular organs, whilst one-D (distributed parameter) models add the facility to represent efficiently the effects of pulse wave transmission in the arterial network at greatly reduced computational expense compared to higher dimensional computational fluid dynamics studies. There is extensive literature on both types of models. Method and Results The purpose of this review article is to summarise published 0D and 1Dmodels of the cardiovascular system, to explore their limitations and range of application, and to provide an indication of the physiological phenomena that can be included in these representations. The review on 0D models collects together in one place a description of the range of models that have been used to describe the various characteristics of cardiovascular response, together with the factors that influence it. Such models generally feature the major components of the system, such as the heart, the heart valves and the vasculature. The models are categorised in terms of the features of the system that they are able to represent, their complexity and range of application: representations of effects including pressure-dependent vessel properties, interaction between the heart chambers, neuro-regulation and auto-regulation are explored. The examination on 1Dmodels covers various methods for the assembly, discretisation and solution of the governing equations, in conjunction with a report of the definition and treatment of boundary conditions. Increasingly, 0D and 1Dmodels are used in multi-scale models, in which their primary role is to provide boundary conditions for sophisticate, and often patient-specific, 2D and 3D models

An analytical solution to the steady-state fluid temperature for 1-D (one dimensional) transpiration cooling has been derived. Transpiration cooling has potential use in the aerospace industry for protection against high heating environments for re-entry vehicles. Literature for analytical treatments of transpiration cooling has been largely confined to the assumption of thermal equilibrium between the porous matrix and fluid. In the present analysis, the fundamental fluid and matrix equations are coupled through a volumetric heat transfer coefficient and investigated in non-thermal equilibrium. The effects of varying the thermal conductivity of the solid matrix and the heat transfer coefficient are investigated. The results are also compared to existing experimental data.

The non-steady-state formation of small clusters and the growth of grains accompanied by chemical reactions are formulated under the consideration that the collision of key gas species (key molecule) controls the kinetics of dust formation process. The formula allows us to evaluate the size distribution and condensation efficiency of dust formed in astrophysical environments. We apply the formulation to the formation of C and MgSiO{sub 3} grains in the ejecta of supernovae, as an example, to investigate how the non-steady effect influences the formation process, condensation efficiency f{sub con,{sub ∞}}, and average radius a{sub ave,{sub ∞}} of newly formed grains in comparison with the results calculated with the steady-state nucleation rate. We show that the steady-state nucleation rate is a good approximation if the collision timescale of key molecule τ{sub coll} is much smaller than the timescale τ{sub sat} with which the supersaturation ratio increases; otherwise the effect of the non-steadystate becomes remarkable, leading to a lower f{sub con,{sub ∞}} and a larger a{sub ave,{sub ∞}}. Examining the results of calculations, we reveal that the steady-state nucleation rate is applicable if the cooling gas satisfies Λ ≡ τ{sub sat}/τ{sub coll} ∼> 30 during the formation of dust, and find that f{sub con,{sub ∞}} and a{sub ave,{sub ∞}} are uniquely determined by Λ{sub on} at the onset time t{sub on} of dust formation. The approximation formulae for f{sub con,{sub ∞}} and a{sub ave,{sub ∞}} as a function of Λ{sub on} could be useful in estimating the mass and typical size of newly formed grains from observed or model-predicted physical properties not only in supernova ejecta but also in mass-loss winds from evolved stars.

Previously we have developed a mathematical model of radon adsorption in active air with water vapor on small U.S. Environmental Protection Agency charcoal canisters that are used for environmental measurements of radon. The purpose of this paper is to extend this mathematical model to describe the adsorption of radon by large charcoal beds with radon-laden air flowing through them. The resulting model equations are solved analytically to predict the steady-state adsorption of radon by such beds. 14 refs., 3 figs.

GTCVI is a finite volume model for steady-state simulation of forced-flow chemical vapor infiltration in either Cartesian or cylindrical coordinates. The model solves energy and momentum balances simultaneously over a given domain discretized into an array of finite volume elements. The species balances and deposition rates are determined after the energy and momentum balances converge. Density-dependent preform properties are included in the model. Transient average density, backpressure, temperature gradient, and average radial deposition rates canmore » be summarized. Optimal infiltration conditions can be found by varying temperature, flow, and reactant concentration.« less

Within the hydrodynamic modelling community, it is common practice to apply different modelling systems for coastal waters and river systems. Whereas for coastal waters 3D finite difference or finite element grids are commonly used, river systems are generally modelled using 1D networks. Each of these systems is tailored towards specific applications. Three-dimensional coastal water models are designed to model the horizontal and vertical variability in coastal waters and are less well suited for representing the complex geometry and cross-sectional areas of river networks. On the other hand, 1D river network models are designed to accurately represent complex river network geometries and complex structures like weirs, barrages and dams. A disadvantage, however, is that they are unable to resolve complex spatial flow variability. In real life, however, coastal oceans and rivers interact. In deltaic estuaries, both tidal intrusion of seawater into the upstream river network and river discharge into open waters play a role. This is frequently approached by modelling the systems independently, with off-line coupling of the lateral boundary forcing. This implies that the river and the coastal model run sequentially, providing lateral discharge (1D) and water level (3D) forcing to each other without the possibility of direct feedback or interaction between these processes. An additional disadvantage is that due to the time aggregation usually applied to exchanged quantities, mass conservation is difficult to ensure. In this paper, we propose an approach that couples a 3D hydrodynamic modelling system for coastal waters (Delft3D) with a 1Dmodelling system for river hydraulics (SOBEK) online. This implies that contrary to off-line coupling, the hydrodynamic quantities are exchanged between the 1D and 3D domains during runtime to resolve the real-time exchange and interaction between the coastal waters and river network. This allows for accurate and mass conserving

Rainfall-runoff simulations were conducted to estimate the characteristics of the steady-state infiltration rate into 1-m2 north- and south-facing hillslope plots burned by a wildfire in October 2003. Soil profiles in the plots consisted of a two-layer system composed of an ash on top of sandy mineral soil. Multiple rainfall rates (18.4-51.2 mm h-1) were used during 14 short-duration (30 min) and 2 long-duration simulations (2-4 h). Steadystate was reached in 7-26 min. Observed spatially-averaged steady-state infiltration rates ranged from 18.2 to 23.8 mm h-1 for north-facing and from 17.9 to 36.0 mm h-1 for south-facing plots. Three different theoretical spatial distribution models of steady-state infiltration rate were fit to the measurements of rainfall rate and steady-state discharge to provided estimates of the spatial average (19.2-22.2 mm h-1) and the coefficient of variation (0.11-0.40) of infiltration rates, overland flow contributing area (74-90% of the plot area), and infiltration threshold (19.0-26 mm h-1). Tensiometer measurements indicated a downward moving pressure wave and suggest that infiltration-excess overland flow is the runoff process on these burned hillslope with a two-layer system. Moreover, the results indicate that the ash layer is wettable, may restrict water flow into the underlying layer, and increase the infiltration threshold; whereas, the underlying mineral soil, though coarser, limits the infiltration rate. These results of the spatial variability of steady-state infiltration can be used to develop physically-based rainfall-runoff models for burned areas with a two-layer soil system. ?? 2010 Elsevier B.V.

Purpose Previous studies have shown that the onset of high-contrast, fast reversing patterned stimuli induces rapid blood flow increase in retinal vessels in association with slow changes of the steady-state PERG signal. We tested the hypothesis that adaptive PERG changes of normal controls (NC) differed from those of glaucoma suspects (GS) and patients with early manifest glaucoma (EMG). Methods Subjects were 42 GS (SAP MD −0.89 ±1.8 dB), 22 EMG (MD −2.12 ±2.4 dB) with visual acuity of ≥20/20 and 16 age-matched NC from a previous study. The PERG signal was sampled every ~15 s over 4 minutes in response to gratings (1.6 cyc/deg, 100% contrast) reversing 16.28 times/s. Amplitude/phase values of successive PERG samples were fitted with a non-parametric LOWESS smoothing function to retrieve the initial and final values and calculate their difference (delta) and the residual standard deviation around the fitted function (SDr). The magnitude of PERG adaptive change compared to random variability was calculated as log10 of percentage coefficient of variation CoV=100*SDr ÷ |delta|. Grand-average PERGs were also obtained by averaging all samples of the same series. Results The grand-average PERG amplitude (ANOVA, p=0.02), but not phase (ANOVA, p=0.63), decreased with increasing severity of disease. Adaptive changes (log10 (CoV) of PERG amplitude were not significantly associated with disease severity (ANOVA, p=0.27), but adaptive changes (log10 (CoV) of PERG phase were (ANOVA, p=0.037; linear trend, p=0.011). Conclusions The steady-state PERG signal displayed slow adaptive changes over time that could be isolated from random variability. PERG adaptive changes differed from those of grand-average PERGs (corresponding the standard steady-state PERG), thus representing a new source of biological information about retinal ganglion cell function that may have potential in the study of glaucoma and optic nerve diseases. PMID:23429613

Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the η-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.

We propose a new spin-glass model with no positional quenched disorder which is regarded as a coarse-grained model of a structural glass-former. The model is analyzed in the 1D case when the number N of states of a primary cell is large. For N → ∞, the model exhibits a sharp freezing transition of the thermodynamic origin. It is shown both analytically and numerically that the glass transition is accompanied by a significant growth of a static length scale ξ pointing to the structural (equilibrium) nature of dynamical slowdown effects in supercooled liquids.

We propose a new spin-glass model with no positional quenched disorder which is regarded as a coarse-grained model of a structural glass-former. The model is analyzed in the 1D case when the number N of states of a primary cell is large. For N → ∞, the model exhibits a sharp freezing transition of the thermodynamic origin. It is shown both analytically and numerically that the glass transition is accompanied by a significant growth of a static length scale ξ pointing to the structural (equilibrium) nature of dynamical slowdown effects in supercooled liquids. PMID:26233148

We propose a new spin-glass model with no positional quenched disorder which is regarded as a coarse-grained model of a structural glass-former. The model is analyzed in the 1D case when the number N of states of a primary cell is large. For N → ∞, the model exhibits a sharp freezing transition of the thermodynamic origin. It is shown both analytically and numerically that the glass transition is accompanied by a significant growth of a static length scale ξ pointing to the structural (equilibrium) nature of dynamical slowdown effects in supercooled liquids.

The use of one-dimensional hydraulic models currently is the standard method for estimating velocity fields through a bridge opening for scour computations and habitat assessment. Flood-flow contraction through bridge openings, however, is hydrodynamically two dimensional and often three dimensional. Although there is awareness of the utility of two-dimensional models to predict the complex hydraulic conditions at bridge structures, little guidance is available to indicate whether a one- or two-dimensional model will accurately estimate the hydraulic conditions at a bridge site. The U.S. Geological Survey, in cooperation with the North Carolina Department of Transportation, initiated a study in 2004 to compare one- and two-dimensional model results with field measurements at complex riverine and tidal bridges in North Carolina to evaluate the ability of each model to represent field conditions. The field data consisted of discharge and depth-averaged velocity profiles measured with an acoustic Doppler current profiler and surveyed water-surface profiles for two high-flow conditions. For the initial study site (U.S. Highway 13 over the Tar River at Greenville, North Carolina), the water-surface elevations and velocity distributions simulated by the one- and two-dimensional models showed appreciable disparity in the highly sinuous reach upstream from the U.S. Highway 13 bridge. Based on the available data from U.S. Geological Survey streamgaging stations and acoustic Doppler current profiler velocity data, the two-dimensional model more accurately simulated the water-surface elevations and the velocity distributions in the study reach, and contracted-flow magnitudes and direction through the bridge opening. To further compare the results of the one- and two-dimensional models, estimated hydraulic parameters (flow depths, velocities, attack angles, blocked flow width) for measured high-flow conditions were used to predict scour depths at the U.S. Highway 13 bridge by

Many 1-D, field scale crop models over-simplify root growth. The over-simplification of this "hidden half" of the crop may have significant consequences on simulated root water and nutrient uptake with a corresponding reflection on the simulated crop yields. Poor representation of root growth in crop models may therefore constitute a major source of uncertainty propagation. In this study we assess the effect of an improved representation of root growth in a model solution of the model framework SIMPLACE (Scientific Impact assessment and Modeling PLatform for Advanced Crop and Ecosystem management) compared to conventional 1-D approaches. The LINTUL5 crop growth model is coupled to the Hillflow soil water balance model within the SIMPLACE modeling framework (Gaiser et al, 2013). Root water uptake scenarios in the soil hydrological simulator Hillflow (Bronstert, 1995) together with an improved representation of root growth is compared to scenarios for which root growth is simplified. The improvement of root growth is achieved by integrating root growth solutions from R-SWMS (Javaux et al., 2008) into the SIMPLACE model solution. R-SWMS is a three dimensional model for simultaneous modeling of root growth, soil water fluxes and solute transport and uptake. These scenarios are tested by comparing how well the simulated water contents match with the observed soil water dynamics. The impacts of the scenarios on above ground biomass and wheat grain are assessed

Estimation of soil organic carbon (SOC) stock using models typically requires long term spin-up of the carbon-nitrogen (CN) models, which has become a bottleneck for global modeling. We report a new numerical approach to estimate global SOC stock that can alleviate long spin-up. The approach uses satellite-based canopy leaf area index (LAI) and takes advantage of a reaction-based biogeochemical module—Next Generation BioGeoChemical Module (NGBGC) that was recently developed and incorporated in version 4 of the Community Land Model (CLM4). Although NGBGC uses the same CN mechanisms as in CLM4CN, it can be easily configured to run prognostic or steadystate simulations. The new approach was applied at point and global scales and compared with SOC derived from spin-up by running NGBGC in the prognostic mode, and SOC from the Harmonized World Soil Database (HWSD). The steadystate solution is comparable to the spin-up value when the satellite LAI is close to that from the spin-up solution, and largely captured the global variability of the HWSD SOC across the different dominant plant functional types (PFTs). The correlation between the simulated and HWSD SOC was, however, weak at both point and global scales, suggesting the needs for improving the biogeochemical processes described in CLM4 and updating HWSD. Besides SOC, the steadystate solution also includes all other state variables simulated by a spin-up run, which makes the tested approach a promising tool to efficiently estimate global SOC distribution and evaluate and compare multiple aspects simulated by different CN mechanisms in the model.

A two-dimensional transient model is developed to simulate steady-state and transient operations of single-cell thermionic fuel elements (TFEs). Model predictions are in good agreement with published data to within 4.5 and 5.5% for fission and electrically heated TFEs of the TOPAZ-II type, respectively. In addition, the results of a transient analysis simulating the startup of an electrically heated TFE, following a step function increase in thermal power, are in presented and discussed.

We study self-oscillations of an optomechanical system, where coherent mechanical oscillations are induced by a driven optical or microwave cavity, for the case of an anharmonic mechanical oscillator potential. A semiclassical analytical model is developed to characterize the limit cycle for large mechanical amplitudes corresponding to a weak nonlinearity. As a result, we predict conditions to achieve subpoissonian phonon statistics in the steadystate, indicating classically forbidden behavior. We compare with numerical simulations and find very good agreement. Our model is quite general and can be applied to other physical systems such as trapped ions or superconducting circuits.

A new theory has been developed to calculate the steadystate temperature profile in a cylindrical sample positioned along the entire axis of a cylindrical microwave cavity. Temperature profiles where computed for- alumina rods of various radii contained in a cavity excite in one of the TM(sub OnO) modes with n = 1, 2 or 3. Calculations where also performed with a concentric outer cylindrical tube surrounding the rod to investigate hybrid heating. The parameters studies of the sample center and surface temperature where performed as a function of the total power transmitted into the cavity. Also, the total hemispherical emissivity was varied at boundaries of the rod, surrounding tube, and cavity walls. The result are discussed in the context of controlling the average rod temperature and the temperature distribution in the rod during microwave processing.

The results of an extended analysis of the plasma and electric field data of the Pioneer Venus Orbiter (PVO) are presented. The persistent presence of a plasma transition embedded in the flanks of the Venus ionosheath between the bow shock and the ionopause is reported. This transition is identified by the repeated presence of characteristic bursts in the 30 kHz channel of the electric field detector of the PVO. The observed electric field signals coincide with the onset of different plasma conditions in the inner ionosheath where more rarified plasma fluxes are measured. The repeated identification of this intermediate ionosheath transition in the PVO data indicates that it is present as a steadystate feature of the Venus plasma environment. The distribution of PVO orbits in which the transition is observed suggests that it is more favorably detected in the vicinity of and downstream from the terminator.

The CT injector originally used for injecting CTs into 1T toroidal field discharges in the TdeV tokamak was shipped PPPL from the Affiliated Customs Brokers storage facility in Montreal during November 2002. All components were transported safely, without damage, and are currently in storage at PPPL, waiting for further funding in order to begin advanced fueling experiments on NSTX. The components are currently insured through the University of Washington. Several technical presentations were made to investigate the feasibility of the CT injector installation on NSTX. These technical presentations, attached to this document, were: (1) Motivation for Compact Toroida Injection in NSTX; (2) Assessment of the Engineering Feasibility of Installing CTF-II on NSTX; (3) Assessment of the Cost for CT Installation on NSTX--A Peer Review; and (4) CT Fueling for NSTX FY 04-08 steady-state operation needs.

An analytic expression is presented for the effective dispersion coefficient in the case where a solute is focused in a parabolic flow against a linear gradient in a restoring force. This expression was derived by employing a minor variation on the method of moments used by Aris in his development of the dispersion coefficients for a time-dependent, isocratic system. In the present case, dispersion is controlled by two dimensionless groups, a Peclet number which is proportional to the parabolic component of the flow, and a gradient number which is proportional to the slope of the restoring force. These results confirm that the Aris-Taylor expression for the dispersion coefficient should not be applied in cases where a solute is focused to a stationary steadystate. PMID:25521436

Conventional methods for evaluating some characteristic values of nuclides relating to burnup in a given neutron spectrum are reviewed in a mathematically systematic way, and a new method based on the importance theory is proposed. In this method, these characteristic values of a nuclide are equivalent to the importances of the nuclide. By solving the equation adjoint to the steady-state burnup equation with a properly chosen source term, the importances for all nuclides are obtained simultaneously.The fission number importance, net neutron importance, fission neutron importance, and absorbed neutron importance are evaluated and discussed. The net neutron importance is a measure directly estimating neutron economy, and it can be evaluated simply by calculating the fission neutron importance minus the absorbed neutron importance, where only the absorbed neutron importance depends on the fission product. The fission neutron importance and absorbed neutron importance are analyzed separately, and detailed discussions of the fission product effects are given for the absorbed neutron importance.

The auditory steady-state responses (ASSR) is quite a new method of electrophysiological threshold estimation with no clinical standards. It was the aim of this study to review practical and theoretical thesis of ASSR and mention recent recommendations and achievements of this technique. The most common application of ASSR is diagnosis of hearing loss in children together with ABR test. In this paper we mentioned information about influence of physiological factors (age, sex, state of arousal, handedness) and type of recording technique (electrodes placement, air and bone stimulation, occlusion effect, amplitude and frequency stimulation, multiple or single frequency stimulation, dichotic and monotic recording technique and type of hearing loss) on ASSR. We conclude that putting ASSR in clinical use as an standardized method it is necessary to do research with numerous groups of patients using the same equipment and parameters of tests. PMID:21166136

The first combined experimental and theoretical studies of dust remobilization by plasma forces are reported. The main theoretical aspects of remobilization in fusion devices under steadystate conditions are analyzed. In particular, the dominant role of adhesive forces is highlighted and generic remobilization conditions—direct lift-up, sliding, rolling—are formulated. A novel experimental technique is proposed, based on controlled adhesion of dust grains on tungsten samples combined with detailed mapping of the dust deposition profile prior and post plasma exposure. Proof-of-principle experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are presented. The versatile environment of the linear device Pilot-PSI allowed for experiments with different magnetic field topologies and varying plasma conditions that were complemented with camera observations.